AAV-Mediated expression of galactocerebrosidase in brain results in attenuated symptoms and extended life span in murine models of globoid cell leukodystrophy

Brain Targeted AAV1-GALC Gene Therapy Reduces Psychosine and Extends Lifespan in a Mouse Model of Krabbe Disease

Krabbe disease (KD) is a progressive and devasting neurological disorder that leads to the toxic accumulation of psychosine in the white matter of the central nervous system (CNS). The condition is inherited via biallelic, loss-of-function mutations in the galactosylceramidase (GALC) gene. To rescue GALC gene function in the CNS of the twitcher mouse model of KD, an adeno-associated virus serotype 1 vector expressing murine GALC under control of a chicken β-actin promoter (AAV1-GALC) was administered to newborn mice by unilateral intracerebroventricular injection. AAV1-GALC treatment significantly improved body weight gain and survival of the twitcher mice (n = 8) when compared with untreated controls (n = 5). The maximum weight gain after postnatal day 10 was significantly increased from 81% to 217%. The median lifespan was extended from 43 days to 78 days (range: 74-88 days) in the AAV1-GALC-treated group. Widespread expression of GALC protein and alleviation of KD neuropathology were detected in the CNS of the treated mice when examined at the moribund stage. Functionally, elevated levels of psychosine were completely normalized in the forebrain region of the treated mice. In the posterior region, which includes the mid- and the hindbrain, psychosine was reduced by an average of 77% (range: 53-93%) compared to the controls. Notably, psychosine levels in this region were inversely correlated with body weight and lifespan of AAV1-GALC-treated mice, suggesting that the degree of viral transduction of posterior brain regions following ventricular injection determined treatment efficacy on growth and survivability, respectively. Overall, our results suggest that viral vector delivery via the cerebroventricular system can partially correct psychosine accumulation in brain that leads to slower disease progression in KD.

Identifying altered developmental pathways in human globoid cell leukodystrophy iPSCs-derived NSCs using transcriptome profiling

BACKGROUND

Globoid cell leukodystrophy (GLD) is a devastating neurodegenerative disease characterized by widespread demyelination caused by galactocerebrosidase defects. Changes in GLD pathogenesis occurring at the molecular level have been poorly studied in human-derived neural cells. Patient-derived induced pluripotent stem cells (iPSCs) are a novel disease model for studying disease mechanisms and allow the generation of patient-derived neuronal cells in a dish.

RESULTS

In this study, we identified gene-expression changes in iPSCs and iPSC-derived neural stem cells (NSCs) from a patient with GLD (K-iPSCs/NSCs) and normal control (AF-iPSCs/NSCs), in order to investigate the potential mechanism underlying GLD pathogenesis. We identified 194 (K-iPSCs vs. AF-iPSCs) and 702 (K-NSCs vs. AF-NSCs) significantly dysregulated mRNAs when comparing the indicated groups. We also identified dozens of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway terms that were enriched for the differentially expressed genes. Among them, 25 differentially expressed genes identified by RNA-sequencing analysis were validated using real-time quantitative polymerase chain reaction analysis. Dozens of pathways involved in neuroactive ligand-receptor interactions, synaptic vesicle cycle signaling, serotonergic synapse signaling, phosphatidylinositol-protein kinase B signaling, and cyclic AMP signaling were identified as potential contributors to GLD pathogenesis.

CONCLUSIONS

Our results correspond to the fact that mutations in the galactosylceramidase gene may disrupt the identified signaling pathways during neural development, suggesting that alterations in signaling pathways contribute to GLD pathogenesis. At the same time, our results demonstrates that the model based on K-iPSCs is a novel tool that can be used to study the underlying molecular basis of GLD.

Various AAV Serotypes and Their Applications in Gene Therapy: An Overview

Despite scientific discoveries in the field of gene and cell therapy, some diseases still have no effective treatment. Advances in genetic engineering methods have enabled the development of effective gene therapy methods for various diseases based on adeno-associated viruses (AAVs). Today, many AAV-based gene therapy medications are being investigated in preclinical and clinical trials, and new ones are appearing on the market. In this article, we present a review of AAV discovery, properties, different serotypes, and tropism, and a following detailed explanation of their uses in gene therapy for disease of different organs and systems.

Preclinical studies in Krabbe disease: A model for the investigation of novel combination therapies for lysosomal storage diseases

Krabbe disease (KD) is a lysosomal storage disease (LSD) caused by mutations in the galc gene. There are over 50 monogenetic LSDs, which largely impede the normal development of children and often lead to premature death. At present, there are no cures for LSDs and the available treatments are generally insufficient, short acting, and not without co-morbidities or long-term side effects. The last 30 years have seen significant advances in our understanding of LSD pathology as well as treatment options. Two gene therapy-based clinical trials, NCT04693598 and NCT04771416, for KD were recently started based on those advances. This review will discuss how our knowledge of KD got to where it is today, focusing on preclinical investigations, and how what was discovered may prove beneficial for the treatment of other LSDs.

A neglected neurodegenerative disease: Adult-onset globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD), or Krabbe disease (KD) is a rare neurodegenerative disease, and adult-onset GLD is more even neglected by clinicians. This review provides detailed discussions of the serum enzymes, genes, clinical manifestations, neuroimaging features, and therapies of GLD, with particular emphasis on the characteristics of adult-onset GLD, in an attempt to provide clinicians with in-depth insights into this disease.

Efficacy and Safety of a Krabbe Disease Gene Therapy

Krabbe disease is a lysosomal storage disease caused by mutations in the gene that encodes galactosylceramidase, in which galactosylsphingosine (psychosine) accumulation drives demyelination in the central and peripheral nervous systems, ultimately progressing to death in early childhood. Gene therapy, alone or in combination with transplant, has been developed for almost two decades in mouse models, with increasing therapeutic benefit paralleling the improvement of next-generation adeno-associated virus (AAV) vectors. This effort has recently shown remarkable efficacy in the canine model of the disease by two different groups that used either systemic or cerebrospinal fluid (CSF) administration of AAVrh10 or AAV9. Building on our experience developing CSF-delivered, AAV-based drug products for a variety of neurodegenerative disorders, we conducted efficacy, pharmacology, and safety studies of AAVhu68 delivered to the CSF in two relevant natural Krabbe animal models, and in nonhuman primates. In newborn Twitcher mice, the highest dose (1 × 10¹¹ genome copies [GC]) of AAVhu68.hGALC injected into the lateral ventricle led to a median survival of 130 days compared to 40.5 days in vehicle-treated mice. When this dose was administered intravenously, the median survival was 49 days. A single intracisterna magna injection of AAVhu68.cGALC at 3 × 10¹³ GC into presymptomatic Krabbe dogs increased survival for up to 85 weeks compared to 12 weeks in controls. It prevented psychosine accumulation in the CSF, preserved peripheral nerve myelination, ambulation, and decreased brain neuroinflammation and demyelination, although some regions remained abnormal. In a Good Laboratory Practice-compliant toxicology study, we administered the clinical candidate into the cisterna magna of 18 juvenile rhesus macaques at 3 doses that displayed efficacy in mice. We observed no dose-limiting toxicity and sporadic minimal degeneration of dorsal root ganglia (DRG) neurons. Our studies demonstrate the efficacy, scalability, and safety of a single cisterna magna AAVhu68 administration to treat Krabbe disease. ClinicalTrials.Gov ID: NCT04771416.

Krabbe disease: A personal perspective and hypothesis

Introduction: Krabbe disease (KD) or globoid cell leukodystrophy (GLD) is one of the lysosomal disorders affecting central and peripheral nervous systems (CNS and PNS). It is caused by mutations on the galactocerebrosidase (GALC) gene. Affected individuals accumulate undegraded substrates and suffer from neuroinflammation. Methods: Hematopoietic stem cell transplantation (HSCT) has been partially successful in treating patients with KD when accomplished prior to the onset of symptoms. The success is credited to the ability of the hematopoietic stem cells in providing some GALC enzyme to the CNS and eradicating potential neuroinflammation. Combination of the HSCT with some other GALC-providing strategies has shown synergistic effects in the treatment of the mouse model of this disease. Results: Here, the possibility of eliminating HSCT in the treatment of human patients and replacing it with a single therapy that will provide sufficient GALC enzyme to the nervous systems is suggested. Such treatment, if started during the asymptomatic stage of the disease, not only may eradicate the enzyme deficiency, but may also keep any neuroinflammation at bay. Conclusion: Successful treatment of the KD may be possible by restoring consistent and sufficient GALC expression in CNS and PNS.

Krabbe Disease: Prospects of Finding a Cure Using AAV Gene Therapy

Krabbe Disease (KD) is an autosomal metabolic disorder that affects both the central and peripheral nervous systems. It is caused by a functional deficiency of the lysosomal enzyme, galactocerebrosidase (GALC), resulting in an accumulation of the toxic metabolite, psychosine. Psychosine accumulation affects many different cellular pathways, leading to severe demyelination. Although there is currently no effective therapy for Krabbe disease, recent gene therapy-based approaches in animal models have indicated a promising outlook for clinical treatment. This review highlights recent findings in the pathogenesis of Krabbe disease, and evaluates AAV-based gene therapy as a promising strategy for treating this devastating pediatric disease.

Advances in the Diagnosis and Treatment of Krabbe Disease

Krabbe disease is an autosomal recessive leukodystrophy caused by pathogenic variants in the galactocerebrosidase (GALC) gene. GALC activity is needed for the lysosomal hydrolysis of galactosylceramide, an important component of myelin. While most patients are infants, older patients are also diagnosed. Starting in 1970, a diagnosis could be made by measuring GALC activity in leukocytes and cultured cells. After the purification of GALC in 1993, the cDNA and genes were cloned. Over 260 disease-causing variants as well as activity lowering benign variants have been identified. While some pathogenic variants can be considered "severe," others can be considered "mild." The combination of alleles determines the type of Krabbe disease a person will have. To identify patients earlier, newborn screening (NBS) has been implemented in several states. Low GALC activity in this screening test may indicate a diagnosis of Krabbe disease. Second tier testing as well as neuro-diagnostic studies may be required to identify those individuals needing immediate treatment. Treatment of pre-symptomatic or mildly symptomatic patients at this time is limited to hematopoietic stem cell transplantation. Treatment studies using the mouse and dog models have shown that combining bone marrow transplantation with intra-venous gene therapy provides the best outcomes in terms of survival, behavior, and preservation of normal myelination in the central and peripheral nervous systems. With earlier diagnosis of patients through newborn screening and advances in treatment, it is hoped that more patients will have a much better quality of life.

Extracellular Vesicle Proteome of Breast Cancer Patients with and Without Cognitive Impairment Following Anthracycline-based Chemotherapy: An Exploratory Study

Cognitive impairment due to cancer and its therapy is a major concern among cancer patients and survivors. Extracellular vesicle (EVs) composition altered by cancer and chemotherapy may affect neurological processes such as neuroplasticity, potentially impacting the cognitive abilities of cancer patients and survivors. We investigated the EV proteome of breast cancer patients with and without cognitive impairment following anthracycline-based chemotherapy from longitudinally collected plasma. EVs were cup-shaped and positive for Flotillin-1 and TSG-101. We identified 517 differentially expressed EV proteins between the cognitive impaired and non-impaired groups during and post-chemotherapy. The observed decreased expression of p2X purinoceptor, cofilin-1, ADAM 10, and dynamin-1 in the plasma EVs of the cognitive impaired group may suggest alterations in the mechanisms underlying synaptic plasticity. The reduced expression of tight junction proteins among cognitive-impaired patients may imply weakening of the blood-brain barrier. These EV protein signatures may serve as a fingerprint that underscores the mechanisms underlying cognitive impairment in cancer patients and survivors.

Krabbe disease: New hope for an old disease

Krabbe disease (globoid cell leukodystrophy) is a lysosomal storage disease (LSD) characterized by progressive and profound demyelination. Infantile, juvenile and adult-onset forms of Krabbe disease have been described, with infantile being the most common. Children with an infantile-onset generally appear normal at birth but begin to miss developmental milestones by six months of age and die by two to four years of age. Krabbe disease is caused by a deficiency of the acid hydrolase galactosylceramidase (GALC) which is responsible for the degradation of galactosylceramides and sphingolipids, which are abundant in myelin membranes. The absence of GALC leads to the toxic accumulation of galactosylsphingosine (psychosine), a lysoderivative of galactosylceramides, in oligodendrocytes and Schwann cells resulting in demyelination of the central and peripheral nervous systems, respectively. Treatment strategies such as enzyme replacement, substrate reduction, enzyme chaperones, and gene therapy have shown promise in LSDs. Unfortunately, Krabbe disease has been relatively refractory to most single-therapy interventions. Although hematopoietic stem cell transplantation can alter the course of Krabbe disease and is the current standard-of-care, it simply slows the progression, even when initiated in pre-symptomatic children. However, the recent success of combinatorial therapeutic approaches in small animal models of Krabbe disease and the identification of new pathogenic mechanisms provide hope for the development of effective treatments for this devastating disease. This review provides a brief history of Krabbe disease and the evolution of single and combination therapeutic approaches and discusses new pathogenic mechanisms and how they might impact the development of more effective treatment strategies.

Gene Therapy for Lysosomal Storage Disorders: Ongoing Studies and Clinical Development

Rare monogenic disorders such as lysosomal diseases have been at the forefront in the development of novel treatments where therapeutic options are either limited or unavailable. The increasing number of successful pre-clinical and clinical studies in the last decade demonstrates that gene therapy represents a feasible option to address the unmet medical need of these patients. This article provides a comprehensive overview of the current state of the field, reviewing the most used viral gene delivery vectors in the context of lysosomal storage disorders, a selection of relevant pre-clinical studies and ongoing clinical trials within recent years.

Can early treatment of twitcher mice with high dose AAVrh10-GALC eliminate the need for BMT?

Introduction: Krabbe disease (KD) is an autosomal recessive disorder caused by mutations in the galactocerebrosidase (GALC) gene resulting in neuro-inflammation and defective myelination in the central and peripheral nervous systems. Most infantile patients present with clinical features before six months of age and die before two years of age. The only treatment available for pre-symptomatic or mildly affected individuals is hematopoietic stem cell transplantation (HSCT). In the animal models, combining bone marrow transplantation (BMT) with gene therapy has shown the best results in disease outcome. In this study, we examine the outcome of gene therapy alone.

Methods: Twitcher (twi) mice used in the study, have a W339X mutation in the GALC gene. Genotype identification of the mice was performed shortly after birth or post-natal day 1 (PND1), using polymerase chain reaction on the toe clips followed by restriction enzyme digestion and electrophoresis. Eight or nine-day-old affected mice were used for gene therapy treatment alone or combined with BMT. While iv injection of 4 × 10¹³ gc/kg of body weight of viral vector was used originally, different viral titers were also used without BMT to evaluate their outcomes.

Results: When the standard viral dose was increased four- and ten-fold (4X and 10X) without BMT, the lifespans were increased significantly. Without BMT the affected mice were fertile, had the same weight and appearance as wild type mice and had normal strength and gait. The brains showed no staining for CD68, a marker for activated microglia/macrophages, and less astrogliosis than untreated twi mice.

Conclusion: Our results demonstrate that, it may be possible to treat human KD patients with high dose AAVrh10 without blood stem cell transplantation which would eliminate the side effects of HSCT.

Conditions for combining gene therapy with bone marrow transplantation in murine Krabbe disease

Introduction: Krabbe disease (KD) is an autosomal recessive lysosomal disorder caused by mutations in the galactocerebrosidase (GALC) gene. This results in defective myelination in the peripheral and central nervous systems due to low GALC activity. Treatment at this time is limited to hematopoietic stem cell transplantation (HSCT) in pre-symptomatic individuals. While this treatment extends the lives of treated individuals, most have difficulty walking by the end of the first decade due to peripheral neuropathy. Studies in the murine model of KD, twitcher (twi) combining bone marrow transplantation (BMT) with AAVrh10-mGALC showed a great extension of life from 40 days to about 400 days, with some living a full life time. Methods: In order to find the optimum conditions for dosing and timing of this combined treatment, twi mice were injected with five doses of AAVrh10-mGALC at different times after BMT. Survival, as well as GALC expression were monitored along with studies of sciatic nerve myelination and possible liver pathology. Results: Dosing had a pronounced effect on survival and measured GALC activity. There was window of time after BMT to inject the viral vector and see similar results, however delaying both the BMT and the viral injection shortened the lifespans of the treated mice. Lowering the viral dose too much decreased the correction of the sciatic nerve myelination. There was no evidence for hepatic neoplasia. Conclusion: These studies provide the conditions optimum for successfully treating the murine model of KD. There is some flexibility in dosing and timing to obtain a satisfactory outcome. These studies are critical to the planning of a human trial combining the "standard of care", HSCT, with a single iv injection of AAVrh10-GALC.

An Engineered Galactosylceramidase Construct Improves AAV Gene Therapy for Krabbe Disease in Twitcher Mice

Krabbe disease is an inherited neurodegenerative disease caused by mutations in the galactosylceramidase gene. In the infantile form, patients die before 3 years of age. Systemic adeno-associated virus serotype 9 (AAV9) gene therapy was recently shown to reverse the disease course in human patients in another lethal infantile neurodegenerative disease. To explore AAV9 therapy for Krabbe disease, we engineered a codon-optimized AAV9 galactosylceramidase vector. We further incorporated features to allow AAV9-derived galactosylceramidase to more efficiently cross the blood-brain barrier and be secreted from transduced cells. We tested the optimized vector by a single systemic injection in the twitcher mouse, an authentic Krabbe disease model. Untreated twitcher mice showed characteristic neuropathology and motion defects. They died prematurely with a median life span of 41 days. Intravenous injection in 2-day-old twitcher mice reduced central and peripheral neuropathology and significantly improved the gait pattern and body weight. Noticeably, the median life span was extended to 150 days. Intraperitoneal injection in 6- to 12-day-old twitcher mice also significantly improved the motor function, body weight, and median life span (to 104 days). Our results far exceed the ≤70 days median life span seen in all reported stand-alone systemic AAV therapies. Our study highlights the importance of vector engineering for Krabbe disease gene therapy. The engineered vector warrants further development.

M3RNA Drives Targeted Gene Delivery in Acute Myocardial Infarction

IMPACT STATEMENT

The M³RNA (microencapsulated modified messenger RNA) platform is an approach to deliver messenger RNA (mRNA) in vivo, achieving a nonintegrating and viral-free approach to gene therapy. This technology was, in this study, tested for its utility in the myocardium, providing a unique avenue for targeted gene delivery into the freshly infarcted myocardial tissue. This study provides the evidentiary basis for the use of M³RNA in the heart through depiction of its performance in cultured cells, healthy rodent myocardium, and acutely injured porcine hearts. By testing the technology in large animal models of infarction, compatibility of M³RNA with current coronary intervention procedures was verified.

Trehalose reduces retinal degeneration, neuroinflammation and storage burden caused by a lysosomal hydrolase deficiency

The accumulation of undegraded molecular material leads to progressive neurodegeneration in a number of lysosomal storage disorders (LSDs) that are caused by functional deficiencies of lysosomal hydrolases. To determine whether inducing macroautophagy/autophagy via small-molecule therapy would be effective for neuropathic LSDs due to enzyme deficiency, we treated a mouse model of mucopolysaccharidosis IIIB (MPS IIIB), a storage disorder caused by deficiency of the enzyme NAGLU (alpha-N-acetylglucosaminidase [Sanfilippo disease IIIB]), with the autophagy-inducing compound trehalose. Treated naglu^{–/ –} mice lived longer, displayed less hyperactivity and anxiety, retained their vision (and retinal photoreceptors), and showed reduced inflammation in the brain and retina. Treated mice also showed improved clearance of autophagic vacuoles in neuronal and glial cells, accompanied by activation of the TFEB transcriptional network that controls lysosomal biogenesis and autophagic flux. Therefore, small-molecule-induced autophagy enhancement can improve the neurological symptoms associated with a lysosomal enzyme deficiency and could provide a viable therapeutic approach to neuropathic LSDs.

Abbreviations: ANOVA: analysis of variance; Atg7: autophagy related 7; AV: autophagic vacuoles; CD68: cd68 antigen; ERG: electroretinogram; ERT: enzyme replacement therapy; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary acidic protein; GNAT2: guanine nucleotide binding protein, alpha transducing 2; HSCT: hematopoietic stem cell transplantation; INL: inner nuclear layer; LC3: microtubule-associated protein 1 light chain 3 alpha; MPS: mucopolysaccharidoses; NAGLU: alpha-N-acetylglucosaminidase (Sanfilippo disease IIIB); ONL: outer nuclear layer; PBS: phosphate-buffered saline; PRKCA/PKCα: protein kinase C, alpha; S1BF: somatosensory cortex; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TFEB: transcription factor EB; VMP/VPL: ventral posterior nuclei of the thalamus

AAVrh10 Gene Therapy Ameliorates Central and Peripheral Nervous System Disease in Canine Globoid Cell Leukodystrophy (Krabbe Disease)

Globoid cell leukodystrophy (GLD), or Krabbe disease, is an inherited, neurologic disorder that results from deficiency of a lysosomal enzyme, galactosylceramidase. Most commonly, deficits of galactosylceramidase result in widespread central and peripheral nervous system demyelination and death in affected infants typically by 2 years of age. Hematopoietic stem-cell transplantation is the current standard of care in children diagnosed prior to symptom onset. However, disease correction is incomplete. Herein, the first adeno-associated virus (AAV) gene therapy experiments are presented in a naturally occurring canine model of GLD that closely recapitulates the clinical disease progression, neuropathological alterations, and biochemical abnormalities observed in human patients. Adapted from studies in twitcher mice, GLD dogs were treated by combination intravenous and intracerebroventricular injections of AAVrh10 to target both the peripheral and central nervous systems. Combination of intravenous and intracerebroventricular AAV gene therapy had a clear dose response and resulted in delayed onset of clinical signs, extended life-span, correction of biochemical defects, and attenuation of neuropathology. For the first time, therapeutic effect has been established in the canine model of GLD by targeting both peripheral and central nervous system impairments with potential clinical implications for GLD patients.

Intrathecal administration of AAV/GALC vectors in 10-11-day-old twitcher mice improves survival and is enhanced by bone marrow transplant

Globoid cell leukodystrophy (GLD), or Krabbe disease, is an autosomal recessive neurodegenerative disease caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). Hematopoietic stem cell transplantation (HSCT) provides modest benefit in presymptomatic patients but is well short of a cure. Gene transfer experiments using viral vectors have shown some success in extending the survival in the mouse model of GLD, twitcher mice. The present study compares three single-stranded (ss) AAV serotypes, two natural and one engineered (with oligodendrocyte tropism), and a self-complementary (sc) AAV vector, all packaged with a codon-optimized murine GALC gene. The vectors were delivered via a lumbar intrathecal route for global CNS distribution on PND10-11 at a dose of 2 × 10(11) vector genomes (vg) per mouse. The results showed a similar significant extension of life span of the twitcher mice for all three serotypes (AAV9, AAVrh10, and AAV-Olig001) as well as the scAAV9 vector, compared to control cohorts. The rAAV gene transfer facilitated GALC biodistribution and detectable enzymatic activity throughout the CNS as well as in sciatic nerve and liver. When combined with BMT from syngeneic wild-type mice, there was significant improvement in survival for ssAAV9. Histopathological analysis of brain, spinal cord, and sciatic nerve showed significant improvement in preservation of myelin, with ssAAV9 providing the greatest benefit. In summary, we demonstrate that lumbar intrathecal delivery of rAAV/mGALCopt can significantly enhance the life span of twitcher mice treated at PND10-11 and that BMT synergizes with this treatment to improve the survival further. © 2016 Wiley Periodicals, Inc.

Perspective on innovative therapies for globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD), or Krabbe's disease, is a lysosomal storage disorder resulting from deficiency of the lysosomal hydrolase galactosylceramidase. The infantile forms are characterized by a unique relentless and aggressive progression with a wide range of neurological symptoms and complications. Here we review and discuss the basic concepts and the novel mechanisms identified as key contributors to the peculiar GLD pathology, highlighting their therapeutic implications. Then, we evaluate evidence from extensive experimental studies on GLD animal models that have highlighted fundamental requirements to obtain substantial therapeutic benefit, including early and timely intervention, high levels of enzymatic reconstitution, and global targeting of affected tissues. Continuous efforts in understanding GLD pathophysiology, the interplay between various therapies, and the mechanisms of disease correction upon intervention may allow advancing research with innovative approaches and prioritizing treatment strategies to develop more efficacious treatments. © 2016 Wiley Periodicals, Inc.

Krabbe disease: One Hundred years from the bedside to the bench to the bedside

This Review summarizes the progress in understanding the pathogenesis and treatment of Krabbe disease from the description of five patients in by Knud Krabbe until 2016. To determine the cause of this genetic disease, pathological and chemical analyses of tissues from the nervous systems of patients were performed. It was determined that these patients had a pathological feature known as globoid cell in the brain and that this consisted partially of galactosylceramide, a major sphingolipid component of myelin. The finding that these patients had a deficiency of galactocerebrosidase (GALC) activity opened the way to relatively simple diagnostic testing with easily obtainable tissue samples, studies leading to the purification of GALC, and cloning of the GALC cDNA and gene. The availability of the gene sequence led to the identification of mutations in patients and to the current studies involving the use of viral vectors containing the GALC cDNA to treat experimentally naturally occurring animal models, such as twitcher mice. Currently, treatment of presymptomatic human patients is limited to hematopoietic stem cell transplantation (HSCT). With recent studies showing successful treatment of animal models with a combination of HSCT and viral gene therapy, it is hoped that more effective treatments will soon be available for human patients. For this Review, it is not possible to reference all of the articles contributing to our current state of knowledge about this disease; however, we have chosen those that have influenced our studies by suggesting research paths to pursue. © 2016 Wiley Periodicals, Inc.

Gene therapy for metachromatic leukodystrophy

Leukodystrophies (LDs) are rare, often devastating genetic disorders with neurologic symptoms. There are currently no disease-specific therapeutic approaches for these diseases. In this review we use metachromatic leukodystrophy as an example to outline in the brief the therapeutic approaches to MLD that have been tested in animal models and in clinical trials, such as enzyme-replacement therapy, bone marrow/umbilical cord blood transplants, ex vivo transplantation of genetically modified hematopoietic stem cells, and gene therapy. These studies suggest that to be successful the ideal therapy for MLD must provide persistent and high level expression of the deficient gene, arylsulfatase A in the CNS. Gene therapy using adeno-associated viruses is therefore the ideal choice for clinical development as it provides the best balance of potential for efficacy with reduced safety risk. Here we have summarized the published preclinical data from our group and from others that support the use of a gene therapy with AAVrh.10 serotype for clinical development as a treatment for MLD, and as an example of the potential of gene therapy for LDs especially for Krabbe disease, which is the focus of this special issue. © 2016 Wiley Periodicals, Inc.

Immunological considerations for treating globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD, or Krabbe's disease) is a severe inherited neurodegenerative disease caused by the lack of a lysosomal enzyme, GALC. The disease has been characterized in humans as well as three naturally occurring animal models, murine, canine, and nonhuman primate. Multiple treatment strategies have been explored for GLD, including enzyme replacement therapy, small-molecule pharmacological approaches, gene therapy, and bone marrow transplant. No single therapeutic approach has proved to be entirely effective, and the reason for this is not well understood. It is unclear whether initiation of a neuroinflammatory cascade in GLD precedes demyelination, a hallmark of the disease, but it does precede overt symptoms. This Review explores what is known about the role of inflammation and the immune response in the progression of GLD as well as how various treatment strategies might interplay with innate and adaptive immune responses involved in GLD. The focus of this Review is on GLD, but these concepts may have relevance for other, related diseases. © 2016 Wiley Periodicals, Inc.

Destination Brain: the Past, Present, and Future of Therapeutic Gene Delivery

Neurological diseases and disorders (NDDs) present a significant societal burden and currently available drug- and biological-based therapeutic strategies have proven inadequate to alleviate it. Gene therapy is a suitable alternative to treat NDDs compared to conventional systems since it can be tailored to specifically alter select gene expression, reverse disease phenotype and restore normal function. The scope of gene therapy has broadened over the years with the advent of RNA interference and genome editing technologies. Consequently, encouraging results from central nervous system (CNS)-targeted gene delivery studies have led to their transition from preclinical to clinical trials. As we shift to an exciting gene therapy era, a retrospective of available literature on CNS-associated gene delivery is in order. This review is timely in this regard, since it analyzes key challenges and major findings from the last two decades and evaluates future prospects of brain gene delivery. We emphasize major areas consisting of physiological and pharmacological challenges in gene therapy, function-based selection of a ideal cellular target(s), available therapy modalities, and diversity of viral vectors and nanoparticles as vehicle systems. Further, we present plausible answers to key questions such as strategies to circumvent low blood-brain barrier permeability and most suitable CNS cell types for targeting. We compare and contrast pros and cons of the tested viral vectors in the context of delivery systems used in past and current clinical trials. Gene vector design challenges are also evaluated in the context of cell-specific promoters. Key challenges and findings reported for recent gene therapy clinical trials, assessing viral vectors and nanoparticles are discussed from the perspective of bench to bedside gene therapy translation. We conclude this review by tying together gene delivery challenges, available vehicle systems and comprehensive analyses of neuropathogenesis to outline future prospects of CNS-targeted gene therapies.

Lysosomal Re-acidification Prevents Lysosphingolipid-Induced Lysosomal Impairment and Cellular Toxicity

Neurodegenerative lysosomal storage disorders (LSDs) are severe and untreatable, and mechanisms underlying cellular dysfunction are poorly understood. We found that toxic lipids relevant to three different LSDs disrupt multiple lysosomal and other cellular functions. Unbiased drug discovery revealed several structurally distinct protective compounds, approved for other uses, that prevent lysosomal and cellular toxicities of these lipids. Toxic lipids and protective agents show unexpected convergence on control of lysosomal pH and re-acidification as a critical component of toxicity and protection. In twitcher mice (a model of Krabbe disease [KD]), a central nervous system (CNS)-penetrant protective agent rescued myelin and oligodendrocyte (OL) progenitors, improved motor behavior, and extended lifespan. Our studies reveal shared principles relevant to several LSDs, in which diverse cellular and biochemical disruptions appear to be secondary to disruption of lysosomal pH regulation by specific lipids. These studies also provide novel protective strategies that confer therapeutic benefits in a mouse model of a severe LSD.

Treatment for Krabbe's disease: Finding the combination

Globoid cell leukodystrophy (GLD) is an autosomal recessive neurodegenerative disorder caused by a deficiency of the lysosomal enzyme galactocerebrosidase (GALC). GALC is responsible for catabolism of certain glycolipids, including the toxic compound galactosylsphingosine (psychosine). Histological signs of disease include the widespread loss of myelin in the central and peripheral nervous systems, profound neruroinflammation, and axonal degeneration. Patients suffering from GLD also display neurological deterioration. Many different individual therapies have been investigated in the murine model of the GLD, the Twitcher mouse, with minimal success. The current standard of care for GLD patients, hematopoietic stem cell transplantation, serves only to delay disease progression and is not an effective cure. However, combination therapies that target different pathogenic mechanisms/pathways have been more effective at reducing histological signs of disease, delaying disease onset, prolonging life span, and improving behavioral/cognitive functions in rodent models of Krabbe's disease. In some cases, dramatic synergy between the various therapies has been observed. © 2016 Wiley Periodicals, Inc.

Myelin repair by transplantation of myelin-forming cells in globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD), or Krabbe disease, is a devastating demyelinating disease that affects both the central and peripheral nervous systems. It is caused by genetic deficiency in the activity of a lysosomal enzyme, galactocerebrosidase (GALC), which is necessary for the maintenance of myelin. Hematopoietic stem cell transplantation (HSCT) including umbilical cord stem cell transplantation is the only effective therapy available to date. HSCT significantly prolongs the life span of patients with GLD when performed before disease onset, although it is not curative. In HSCT, infiltrating donor-derived macrophages are thought to indirectly supply the enzyme (called "cross-correction") to the host's myelinating cells. Given the limitation in treating GLD, it is hypothesized that remyelinating demyelinated axons with GALC-competent myelinating cells by transplantation will result in more stable myelination than endogenous myelin repair supported by GALC cross-correction. Transplantation of myelin-forming cells in a variety of animal models of dysmyelinating and demyelinating disorders suggests that this approach is promising in restoring saltatory conduction and protecting neurons by providing new healthy myelin. However, GLD is one of the most challenging diseases in terms of the aggressiveness of the disease and widespread pathology. Experimental transplantation of myelin-forming cells in the brain of a mouse model of GLD has been only modestly effective to date. Thus, a practical strategy for myelin repair in GLD would be to combine the rapid and widespread cross-correction of GALC by HSCT with the robust, stable myelination provided by transplanted GALC-producing myelin-forming cells. This short review will discuss such possibilities. © 2016 Wiley Periodicals, Inc.

Adeno-Associated Virus-Based Gene Therapy for CNS Diseases

Gene therapy is at the cusp of a revolution for treating a large spectrum of CNS disorders by providing a durable therapeutic protein via a single administration. Adeno-associated virus (AAV)-mediated gene transfer is of particular interest as a therapeutic tool because of its safety profile and efficiency in transducing a wide range of cell types. The purpose of this review is to describe the most notable advancements in preclinical and clinical research on AAV-based CNS gene therapy and to discuss prospects for future development based on a new generation of vectors and delivery.

Widespread Neuronal Transduction of the Rodent CNS via Neonatal Viral Injection

The rapid pace of neuroscience research demands equally efficient and flexible methods for genetically manipulating and visualizing selected neurons within the rodent brain. The use of viral vectors for gene delivery saves the time and cost of traditional germline transgenesis and offers the versatility of readily available reagents that can be easily customized to meet individual experimental needs. Here, we present a protocol for widespread neuronal transduction based on intraventricular viral injection of the neonatal mouse brain. Injections can be done either free-hand or assisted by a stereotaxic device to produce lifelong expression of virally delivered transgenes.

Long-term Improvements in Lifespan and Pathology in CNS and PNS After BMT Plus One Intravenous Injection of AAVrh10-GALC in Twitcher Mice

Krabbe disease is an autosomal recessive disorder resulting from defects in the lysosomal enzyme galactocerebrosidase (GALC). GALC deficiency leads to severe neurological features. The only treatment for presymptomatic infantile patients and later-onset patients is hematopoietic stem cell transplantation (HSCT). This treatment is less than ideal with most patients eventually developing problems with gait and expressive language. Several naturally occurring animal models are available, including twitcher (twi) mice, which have been used for many treatment trials. Previous studies demonstrated that multiple injections of AAVrh10-GALC into the central nervous system (CNS) of neonatal twi mice resulted in significant improvements. Recently we showed that one i.v. injection of AAVrh10-GALC on PND10 resulted in normal GALC activity in the CNS and high activity in the peripheral nervous system (PNS). In the present study, a single i.v. injection of AAVrh10-GALC was given 1 day after bone marrow transplantation (BMT) on PND10. The mice show greatly extended lifespan and normal behavior with improved CNS and PNS findings. Since HSCT is the standard of care in human patients, adding this single i.v. injection of viral vector may greatly improve the treatment outcome.

Enzyme replacement in the CSF to treat metachromatic leukodystrophy in mouse model using single intracerebroventricular injection of self-complementary AAV1 vector

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by a functional deficiency in human arylsulfatase A (hASA). We recently reported that ependymal cells and the choroid plexus are selectively transduced by intracerebroventricular (ICV) injection of adeno-associated virus serotype 1 (AAV1) vector and serve as a biological reservoir for the secretion of lysosomal enzymes into the cerebrospinal fluid (CSF). In the present study, we examined the feasibility of this AAV-mediated gene therapy to treat MLD model mice. Preliminary experiments showed that the hASA level in the CSF after ICV injection of self-complementary (sc) AAV1 was much higher than in mice injected with single-stranded AAV1 or scAAV9. However, when 18-week-old MLD mice were treated with ICV injection of scAAV1, the concentration of hASA in the CSF gradually decreased and was not detectable at 12 weeks after injection, probably due to the development of anti-hASA antibodies. As a result, the sulfatide levels in brain tissues of treated MLD mice were only slightly reduced compared with those of untreated MLD mice. These results suggest that this approach is potentially promising for treating MLD, but that controlling the immune response appears to be crucial for long-term expression of therapeutic proteins in the CSF.

Mitigation of cerebellar neuropathy in globoid cell leukodystrophy mice by AAV-mediated gene therapy

Globoid cell leukodystrophy (GLD) is an autosomal recessive, lysosomal storage disease caused by deficiency of the enzyme galactocerebrosidase (GALC). The absence of GALC activity leads to the accumulation of the toxic substance psychosine and the preferential loss of myelinating cells in the central and peripheral nervous systems. Profound demyelination, astrogliosis and axonopathy are the hallmarks of the pathogenesis of GLD, and cerebellar ataxia is one of the dominant manifestations in adolescents and adults affected with GLD. To date, studies regarding cerebellar degeneration in GLD are limited. In this study, the efficacy of cerebellum-targeted gene therapy on the cerebellar neuropathology in twitcher mice (a murine model of GLD) has been validated. We observed degeneration of Purkinje cells, Bergmann glia, and granule cells in addition to astrocytosis and demyelination in the cerebellum of the twitcher mice. Ultrastructural analysis revealed dark cell degeneration and disintegration of the cellular composition of Purkinje cells in untreated twitcher mice. In addition, the expressions of neurotrophic factors CNTF, GDNF and IGF-I were up-regulated and the expression of BDNF was down-regulated. Intracerebellar-mediated gene therapy efficiently corrected enzymatic deficiency by direct transduction to Purkinje cells and cross-correction in other cell types in the cerebellum, leading to the amelioration of both neuroinflammation and demyelination. The population, dendritic territory, and axonal processes of Purkinje cells remained normal in the cerebellum of treated twitcher mice, where radial fibers of Bergmann glia spanned the molecular layer and collateral branches ensheathed the dendritic processes of Purkinje cells. Moreover, the aberrant expressions of neurotrophic factors were mitigated in the cerebellum of treated twitcher mice, indicating the preservation of cellular function in addition to maintaining the neuronal architecture. The life span of the treated twitcher mice was significantly prolonged and their neurobehavioral performance was improved. Taken together, our findings underscore the complexity of cerebellar neurodegeneration in GLD and highlight the potential effectiveness of gene therapy in mitigating neuropathological deficits in GLD and other neurodegenerative disorders in which Purkinje cells are involved.

Endogenous brain erythropoietin is a potent sex-specific respiratory stimulant in adult and newborn mice

We tested the hypothesis that endogenous brain Epo is a respiratory stimulant. Adult (3 mo) and newborn (10 days) male and female mice received an intracisternal (cisterna magna) injection of soluble Epo receptor (sEpoR; competes with EpoR to bind Epo; 50 μg/ml) or vehicle (0.1% BSA in PBS). Twenty-four hours after injection, we used whole body plethysmography to record minute ventilation (V̇e) tidal volume (VT), respiratory frequency (fR), O2 consumption (V̇o2), and CO2 production (V̇co2) under normoxia and progressive exposure to hypoxia (12-10-6% O2; 10 min each). In adult male and female mice sEpoR decreased normoxic V̇e (-25%), due to a decrease of VT in males and fR in females. Moreover, sEpoR injection decreased the ventilatory response to 12% O2, assessed as V̇e/V̇o2 or V̇e/V̇co2, in male but not in female mice. In newborn male and female mice sEpoR decreased V̇e (-37% in males, -59% in females) and VT (-38% in males, -47% in females) in normoxia and fR in females. During hypoxia, sEpoR decreased V̇e/V̇o2 and V̇e/V̇co2 in mice of both sexes. Upon extreme hypoxia (6% O2), the newborn mice treated with sEpoR showed respiratory depression, signs of asphyxia (gasping) and a high mortality rate in males and females. We concluded that endogenous brain Epo is a potent respiratory stimulant under normoxia and hypoxia in adult and newborn mice. Because sex-specific effects are different in newborn male and female, sex steroids secreted at different ages mice appear to modulate the effects of Epo on respiratory regulation in normoxia and in response to hypoxia.

Intravenous injection of AAVrh10-GALC after the neonatal period in twitcher mice results in significant expression in the central and peripheral nervous systems and improvement of clinical features

Globoid cell leukodystrophy (GLD) or Krabbe disease is an autosomal recessive disorder resulting from the defective lysosomal enzyme galactocerebrosidase (GALC). The lack of GALC enzyme leads to severe neurological symptoms. While most human patients are infants who do not survive beyond 2 years of age, older patients are also diagnosed. In addition to human patients, several naturally occurring animal models, including dog, mouse, and monkey, have also been identified. The mouse model of Krabbe disease, twitcher (twi) mouse has been used for many treatment trials including gene therapy. Using the combination of intracerebroventricular, intracerebellar, and intravenous (iv) injection of the adeno-associated virus serotype rh10 (AAVrh10) expressing mouse GALC in neonate twi mice we previously have demonstrated a significantly extended normal life and exhibition of normal behavior in treated mice. In spite of the prolonged healthy life of these treated mice and improved myelination, it is unlikely that using multiple injection sites for viral administration will be approved for treatment of human patients. In this study, we have explored the outcome of the single iv injection of viral vector at post-natal day 10 (PND10). This has resulted in increased GALC activity in the central nervous system (CNS) and high GALC activity in the peripheral nervous system (PNS). As we have shown previously, an iv injection of AAVrh10 at PND2 results in a small extension of life beyond the typical lifespan of the untreated twi mice (~40 days). In this study, we report that mice receiving a single iv injection at PND10 had no tremor and continued to gain weight until a few weeks before they died. On average, they lived 20-25 days longer than untreated mice. We anticipate that this strategy in combination with other therapeutic options may be beneficial and applicable to treatment of human patients.

History, genetic, and recent advances on Krabbe disease

Krabbe disease or globoid cell leukodystrophy is one of the classic genetic lysosomal storage diseases with autosomal recessive inheritance that affects both central and peripheral nervous systems in several species including humans, rhesus macaques, dogs, mice, and sheep. Since its identification in 1916, lots of scientific investigations were made to define the cause, to evaluate the molecular mechanisms of the damage and to develop more efficient therapies inducing clinical benefit and ameliorating the patients' quality of life. This manuscript gives a historical overview and summarizes the new recent findings about Krabbe disease. Human symptoms and phenotypes, gene encoding for β-galactocerebrosidase and encoded protein were described. Indications about the classical mutations were reported and some specific mutations in restricted geographical area, like the north of Catania City (Italy), were added. Briefly, here we present a mix of past and present investigations on Krabbe disease in order to update the knowledge on its genetic history and molecular mechanisms and to move new scientific investigations.

Therapeutic benefit of lentiviral-mediated neonatal intracerebral gene therapy in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) is an inherited lysosomal storage disease caused by β-galactocerebrosidase (GALC) deficiency. Gene therapy (GT) should provide rapid, extensive and lifetime GALC supply in central nervous system (CNS) tissues to prevent or halt irreversible neurologic progression. Here we used a lentiviral vector (LV) to transfer a functional GALC gene in the brain of Twitcher mice, a severe GLD model. A single injection of LV.GALC in the external capsule of Twitcher neonates resulted in robust transduction of neural cells with minimal and transient activation of inflammatory and immune response. Importantly, we documented a proficient transduction of proliferating and post-mitotic oligodendroglia, a relevant target cell type in GLD. GALC activity (30–50% of physiological levels) was restored in the whole CNS of treated mice as early as 8 days post-injection. The early and stable enzymatic supply ensured partial clearance of storage and reduction of psychosine levels, translating in amelioration of histopathology and enhanced lifespan. At 6 months post-injection in non-affected mice, LV genome persisted exclusively in the injected region, where transduced cells overexpressed GALC. Integration site analysis in transduced brain tissues showed no aberrant clonal expansion and preferential targeting of neural-specific genes. This study establishes neonatal LV-mediated intracerebral GT as a rapid, effective and safe therapeutic intervention to correct CNS pathology in GLD and provides a strong rationale for its application in this and similar leukodystrophies, alone or in combination with therapies targeting the somatic pathology, with the final aim of providing an effective and timely treatment of these global disorders.

HIV Tat Domain Improves Cross-correction of Human Galactocerebrosidase in a Gene- and Flanking Sequence-dependent Manner

Krabbe disease is a devastating neurodegenerative lysosomal storage disorder caused by a deficiency of β-galactocerebrosidase (GALC). Gene therapy is a promising therapeutic approach for Krabbe disease. As the human brain is large and it is difficult to achieve global gene transduction, the efficacy of cross-correction is a critical determinant of the outcome of gene therapy for this disease. We investigated whether HIV Tat protein transduction domain (PTD) can improve the cross-correction of GALC. Tat-PTD significantly increased (~6-fold) cross-correction of GALC through enhanced secretion and uptake in a cell-culture model system. The effects of Tat-PTD were gene and flanking amino acids dependent. Tat-fusion increased the secretion of α-galactosidase A (α-gal A), but this did not improve its cross-correction. Tat-fusion did not change either secretion or uptake of β-glucocerebrosidase (GC). Tat-PTD increased GALC protein synthesis, abolished reactivity of GC to the 8E4 antibody, and likely reduced mannose phosphorylation in all these lysosomal enzymes. This study demonstrated that Tat-PTD can be useful for increasing cross-correction efficiency of lysosomal enzymes. However, Tat-PTD is not a mere adhesive motif but possesses a variety of biological functions. Therefore, the potential beneficial effect of Tat-PTD should be assessed individually on each lysosomal enzyme.Molecular Therapy-Nucleic Acids (2013) 2, e130; doi:10.1038/mtna.2013.57; published online 22 October 2013.

Capsid serotype and timing of injection determines AAV transduction in the neonatal mice brain

Adeno-associated virus (AAV) mediated gene expression is a powerful tool for gene therapy and preclinical studies. A comprehensive analysis of CNS cell type tropism, expression levels and biodistribution of different capsid serotypes has not yet been undertaken in neonatal rodents. Our previous studies show that intracerebroventricular injection with AAV2/1 on neonatal day P0 results in widespread CNS expression but the biodistribution is limited if injected beyond neonatal day P1. To extend these observations we explored the effect of timing of injection on tropism and biodistribution of six commonly used pseudotyped AAVs delivered in the cerebral ventricles of neonatal mice. We demonstrate that AAV2/8 and 2/9 resulted in the most widespread biodistribution in the brain. Most serotypes showed varying biodistribution depending on the day of injection. Injection on neonatal day P0 resulted in mostly neuronal transduction, whereas administration in later periods of development (24–84 hours postnatal) resulted in more non-neuronal transduction. AAV2/5 showed widespread transduction of astrocytes irrespective of the time of injection. None of the serotypes tested showed any microglial transduction. This study demonstrates that both capsid serotype and timing of injection influence the regional and cell-type distribution of AAV in neonatal rodents, and emphasizes the utility of pseudotyped AAV vectors for translational gene therapy paradigms.

Characterization of adipose-derived stromal/stem cells from the Twitcher mouse model of Krabbe disease

Background

Krabbe disease, also known as globoid cell leukodystrophy, is an autosomal recessive neurodegenerative disease caused by the genetic deficiency of galactocerebrosidase (GALC), a lysosomal enzyme responsible for the degradation of several glycosphingolipids like psychosine and galactosylceramide. In order to investigate whether GALC deficiency in Krabbe disease affects adipose-derived stromal/stem cell (ASC) properties and if the ASCs could be used as a source of autologous stem cell therapy for patients with Krabbe disease, ASCs isolated from subcutaneous adipose tissue of Twitcher mice (a murine model of Krabbe disease) and their normal wild type littermates were cultured, expanded, and characterized for their cell morphology, surface antigen expression, osteogenic and adipogenic differentiation, colony forming units, growth kinetics, and immune regulatory capacities in vitro.

Results

ASCs from Twitcher mice (TwiASCs), when compared to ASCs from normal mice (WtASCs), have a reduced osteogenic differentiation potential, have less self-replicating and proliferative capacity, although they have the same fibroblast morphologies and cell sizes. However, surprisingly, the TwiASCs demonstrated similar immune-suppressive capacities as their counterparts WtASCs did when they were transwell co-cultured with macrophages in vitro.

Conclusion

This study reveals that Twitcher ASCs exhibit differences in the biologic potential when compared to their counterparts from normal mice. The changes in Twitcher ASCs may be influenced by the GALC deficiency in Twitcher mice. Nevertheless, none of the changes preclude the use of the TwiASCs for autologous applications.

Bone marrow transplantation increases efficacy of central nervous system-directed enzyme replacement therapy in the murine model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD, Krabbe disease), is an autosomal recessive, neurodegenerative disease caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). In the absence of GALC, the toxic metabolite psychosine accumulates in the brain and causes the death of the myelin-producing cells, oligodendrocytes. Currently, the only therapy for GLD is hematopoietic stem cell transplantation using bone marrow (BMT) or umbilical cord blood. However, this is only partially effective. Previous studies have shown that enzyme replacement therapy (ERT) provides some therapeutic benefit in the murine model of GLD, the Twitcher mouse. Experiments have also shown that two disparate therapies can produce synergistic effects when combined. The current study tests the hypothesis that BMT will increase the therapeutic effects of ERT when these two treatments are combined. Twitcher mice were treated with either ERT alone or both ERT and BMT during the first 2-4 days of life. Recombinant enzyme was delivered by intracerebroventricular (ICV) and intrathecal (IT) injections. Twitcher mice receiving ERT had supraphysiological levels of GALC activity in the brain 24h after injection. At 36 days of age, ERT-treated Twitcher mice had reduced psychosine levels, reduced neuroinflammation, improved motor function, and increased lifespan. Twitcher mice receiving both ERT and BMT had significantly increased lifespan, improved motor function, reduced psychosine levels, and reduced neuroinflammation in certain areas of the brain compared to untreated or ERT-treated Twitcher mice. Together, these results indicate that BMT enhances the efficacy of ERT in GLD.

High-throughput screening of stem cell therapy for globoid cell leukodystrophy using automated neurophenotyping of twitcher mice

Globoid cell leukodystrophy (Krabbe's disease) is an autosomal recessive neurodegenerative disorder that results from the deficiency of galactosylceramidase, a lysosomal enzyme involved in active myelination. Due to the progressive, lethal nature of this disease and the limited treatment options available, multiple laboratories are currently exploring novel therapies using the mouse model of globoid cell leukodystrophy. In order to establish a protocol for motor function assessment of the twitcher mouse, this study tested the capability of an automated system to detect phenotypic differences across mouse genotypes and/or treatment groups. The sensitivity of this system as a screening tool for the assessment of therapeutic interventions was determined by the administration of murine bone marrow-derived stem cells into twitcher mice via intraperitoneal injection. Animal behavior was analyzed using the Noldus EthoVision XT7 software. Novel biomarkers, including abnormal locomotion (e.g., velocity, moving duration, distance traveled, turn angle) and observed behaviors (e.g., rearing activity, number of defecation boli), were established for the twitcher mouse. These parameters were monitored across all mouse groups, and the automated system detected improved locomotion in the treated twitcher mice based on the correction of angular velocity, turn angle, moving duration, and exploratory behavior, such as thigmotaxis. Further supporting these findings, the treated mice showed improved lifespan, gait, wire hang ability, twitching severity and frequency, and sciatic nerve histopathology. Taken together, these data demonstrate the utility of computer-based neurophenotyping for motor function assessment of twitcher mice and support its utility for detecting the efficacy of stem cell-based therapy for neurodegenerative disorders.

The galactocerebrosidase enzyme contributes to maintain a functional neurogenic niche during early post-natal CNS development

We report a novel role for the lysosomal galactosylceramidase (GALC), which is defective in globoid cell leukodystrophy (GLD), in maintaining a functional post-natal subventricular zone (SVZ) neurogenic niche. We show that proliferation/self-renewal of neural stem cells (NSCs) and survival of their neuronal and oligodendroglial progeny are impaired in GALC-deficient mice. Using drugs to modulate inflammation and gene transfer to rescue GALC expression and activity, we show that lipid accumulation resulting from GALC deficiency acts as a cell-autonomous pathogenic stimulus in enzyme-deficient NSCs and progeny before upregulation of inflammatory markers, which later sustain a non-cell-autonomous dysfunction. Importantly, we provide evidence that supply of functional GALC provided by neonatal intracerebral transplantation of NSCs ameliorates the functional impairment in endogenous SVZ cells. Insights into the mechanism/s underlying GALC-mediated regulation of early post-natal neurogenic niches improve our understanding of the multi-component pathology of GLD. The occurrence of a restricted period of SVZ neurogenesis in infancy supports the implications of our study for the development of therapeutic strategies to treat this severe pediatric neurodegenerative disorder.

Extended normal life after AAVrh10-mediated gene therapy in the mouse model of Krabbe disease

Globoid cell leukodystrophy (GLD) or Krabbe disease is a neurodegenerative disorder caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). This deficiency results in accumulation of certain galactolipids including psychosine which is cytotoxic for myelin-producing cells. Treatment of human patients at this time is limited to hematopoietic stem cell transplantation (HSCT) that appears to slow the progression of the disease when performed in presymptomatic patients. In this study, adeno-associated virus (AAV) serotype rh10-(AAVrh10) expressing mouse GALC was used in treating twitcher (twi) mice, the mouse model of GLD. The combination of intracerebroventricular, intracerebellar, and intravenous (iv) injection of viral particles in neonate twi mice resulted in high GALC activity in brain and cerebellum and moderate to high GALC activity in spinal cord, sciatic nerve, and some peripheral organs. Successfully treated mice maintained their weight with no or very little twitching, living up to 8 months. The physical activities of the long-lived treated mice were comparable to wild type for most of their lives. Treated mice showed normal abilities to mate, to deliver pups, to nurse and to care for the newborns. This strategy alone or in combination with other therapeutic options may be applicable to treatment of human patients.

Recombinant adeno-associated viral vectors

Recombinant adeno-associated viral (rAAV) vectors can be used to locally or systemically enhance or silence gene expression. They are relatively nonimmunogenic and can transduce dividing and nondividing cells, and different rAAV serotypes may transduce diverse cell types. Therefore, rAAV vectors are excellent tools to study the function of neuropeptides in local brain areas. In this chapter, we describe a protocol to produce high-titer, in vivo grade, rAAV vector stocks. The protocol includes an Iodixanol gradient, an anion exchange column and a desalting/concentration step and can be used for every serotype. In addition, a short protocol for rAAV injections into the brain and directions on how to detect and localize transduced cells are given.

Neural stem cell gene therapy ameliorates pathology and function in a mouse model of globoid cell leukodystrophy

Murine neural stem cells (mNSCs), either naive or genetically modified to express supranormal levels of β-galactocerebrosidase (GALC), were transplanted into the brain of Twitcher mice, a murine model of globoid cell leukodystrophy, a severe sphingolipidosis. Cells engrafted long-term into the host cytoarchitecture, producing functional GALC. Levels of enzyme activity in brain and spinal cord tissues were enhanced when GALC-overexpressing NSC were used. Enzymatic correction correlated with reduced tissue storage, decreased activation of astroglia and microglia, delayed onset of symptoms, and longer lifespan. Mechanisms underlying the therapeutic effect of mNSC included widespread enzyme distribution, cross-correction of host cells, anti-inflammatory activity, and neuroprotection. Similar cell engraftment and metabolic correction were reproduced using human NSC. Thus, NSC gene therapy rapidly reconstitutes sustained and long-lasting enzyme activity in central nervous system tissues. Combining this approach with treatments targeting the systemic disease associated with leukodystrophies may provide significant therapeutic benefit. Stem Cells 2011;29:1559–1571

Gene and stem cell therapy: alone or in combination?

INTRODUCTION

Both gene and stem cell therapies hold great promise in the treatment of many genetic diseases and are currently focus of interest for many investigators. While both approaches are offering great and valuable treatment options for devastating and life-threatening diseases, they hold much greater promise in combination.

METHODS

As there are multiple options in selecting gene transfer vehicles among the non-viral and viral vectors, there are also many options among the different transplantable cell types ranging from lineage-restricted progenitor cells to multipotent and pluripotent stem cells. Here, combination of the gene therapy and stem cell therapy is discussed.

RESULTS

Several suc-cessful gene and stem cell therapies have been reported both in animal and human trials. Combination of the gene therapy and stem cell therapy can be carried out sequentially where the cell transplantation and the in vivo gene therapy are accomplished one after the other; or, as it is more commonly practiced, they can be carried out as ex vivo gene therapy where the transplantable cells are genetically modified outside the body before being transplanted into the body.

CONCLUSION

The combination of the stem-cell technology with gene therapy has the potential of providing both regenerative tissue and therapeutic material simultaneously; therefore, having the benefits of both technologies.

The myelin mutants as models to study myelin repair in the leukodystrophies

The leukodystrophies are rare and serious genetic disorders of the central nervous system that primarily affect children who frequently die early in life or have significantly delayed motor and mental milestones that result in long-term disability. Although with some of these disorders, early intervention with bone marrow or cord blood transplantation has been proven useful, it has not yet been determined that such therapies promote myelin repair of the central nervous system. Research on experimental therapies aimed at myelin repair is aided by the ability to test cell replacement strategies in genetic models in which the mutations and neuropathology match the human disorder. Thus, models exist of Pelizaeus-Merzbacher disease and the lysosomal storage disorder, Krabbe disease, which reflect the clinical and pathological course of the human disorders. Collectively, animals with mutations in myelin genes are called the myelin mutants, and they include rodent models such as the shiverer mouse that have been extensively used to study myelination by exogenous cell transplantation. These studies have encompassed many permutations of the age of the recipient, type of transplanted cell, site of engraftment, and so forth, and they offer hope that the scaling up of myelin produced by transplanted cells will have clinical significance in treating patients. Here we review these models and discuss their relative importance and use in such translational approaches. We discuss how grafts are identified and functional outcomes are measured. Finally, we briefly discuss the cells that have been successfully transplanted, which may be used in future clinical trials.