Intraventricular administration of recombinant adenovirus to neonatal twitcher mouse leads to clinicopathological improvements

Nanomedicines to treat rare neurological disorders: The case of Krabbe disease

The brain remains one of the most challenging therapeutic targets due to the low and selective permeability of the blood-brain barrier and complex architecture of the brain tissue. Nanomedicines, despite their relatively large size compared to small molecules and nucleic acids, are being heavily investigated as vehicles to delivery therapeutics into the brain. Here we elaborate on how nanomedicines may be used to treat rare neurodevelopmental disorders, using Krabbe disease (globoid cell leukodystrophy) to frame the discussion. As a monogenetic disorder and lysosomal storage disease affecting the nervous system, the lessons learned from examining nanoparticle delivery to the brain in the context of Krabbe disease can have a broader impact on the treatment of various other neurodevelopmental and neurodegenerative disorders. In this review, we introduce the epidemiology and genetic basis of Krabbe disease, discuss current in vitro and in vivo models of the disease, as well as current therapeutic approaches either approved or at different stage of clinical developments. We then elaborate on challenges in particle delivery to the brain, with a specific emphasis on methods to transport nanomedicines across the blood-brain barrier. We highlight nanoparticles for delivering therapeutics for the treatment of lysosomal storage diseases, classified by the therapeutic payload, including gene therapy, enzyme replacement therapy, and small molecule delivery. Finally, we provide some useful hints on the design of nanomedicines for the treatment of rare neurological disorders.

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.

β-Galactosylceramidase Deficiency Causes Upregulation of Long Pentraxin-3 in the Central Nervous System of Krabbe Patients and Twitcher Mice

Globoid cell leukodystrophy (GLD), or Krabbe disease, is a neurodegenerative sphingolipidosis caused by genetic deficiency of lysosomal β-galactosylceramidase (GALC), characterized by neuroinflammation and demyelination of the central (CNS) and peripheral nervous system. The acute phase protein long pentraxin-3 (PTX3) is a soluble pattern recognition receptor and a regulator of innate immunity. Growing evidence points to the involvement of PTX3 in neurodegeneration. However, the expression and role of PTX3 in the neurodegenerative/neuroinflammatory processes that characterize GLD remain unexplored. Here, immunohistochemical analysis of brain samples from Krabbe patients showed that macrophages and globoid cells are intensely immunoreactive for PTX3. Accordingly, Ptx3 expression increases throughout the course of the disease in the cerebrum, cerebellum, and spinal cord of GALC-deficient twitcher (Galc^twi/twi) mice, an authentic animal model of GLD. This was paralleled by the upregulation of proinflammatory genes and M1-polarized macrophage/microglia markers and of the levels of PTX3 protein in CNS and plasma of twitcher animals. Crossing of Galc^twi/twi mice with transgenic PTX3 overexpressing animals (hPTX3 mice) demonstrated that constitutive PTX3 overexpression reduced the severity of clinical signs and the upregulation of proinflammatory genes in the spinal cord of P35 hPTX3/Galc^twi/twi mice when compared to Galc^twi/twi littermates, leading to a limited increase of their life span. However, this occurred in the absence of a significant impact on the histopathological findings and on the accumulation of the neurotoxic metabolite psychosine when evaluated at this late time point of the disease. In conclusion, our results provide the first evidence that PTX3 is produced in the CNS of GALC-deficient Krabbe patients and twitcher mice. PTX3 may exert a protective role by reducing the neuroinflammatory response that occurs in the spinal cord of GALC-deficient animals.

Mechanisms of demyelination and neurodegeneration in globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD), also known as Krabbe disease, is a lysosomal storage disorder causing extensive demyelination in the central and peripheral nervous systems. GLD is caused by loss-of-function mutations in the lysosomal hydrolase, galactosylceramidase (GALC), which catabolizes the myelin sphingolipid galactosylceramide. The pathophysiology of GLD is complex and reflects the expression of GALC in a number of glial and neural cell types in both the central and peripheral nervous systems (CNS and PNS), as well as leukocytes and kidney in the periphery. Over the years, GLD has garnered a wide range of scientific and medical interests, especially as a model system to study gene therapy and novel preclinical therapeutic approaches to treat the spontaneous murine model for GLD. Here, we review recent findings in the field of Krabbe disease, with particular emphasis on novel aspects of GALC physiology, GLD pathophysiology, and therapeutic strategies.

Brainstem development requires galactosylceramidase and is critical for pathogenesis in a model of Krabbe disease

Krabbe disease (KD) is caused by a deficiency of galactosylceramidase (GALC), which induces demyelination and neurodegeneration due to accumulation of cytotoxic psychosine. Hematopoietic stem cell transplantation (HSCT) improves clinical outcomes in KD patients only if delivered pre-symptomatically. Here, we hypothesize that the restricted temporal efficacy of HSCT reflects a requirement for GALC in early brain development. Using a novel Galc floxed allele, we induce ubiquitous GALC ablation (Galc-iKO) at various postnatal timepoints and identify a critical period of vulnerability to GALC ablation between P4-6 in mice. Early Galc-iKO induction causes a worse KD phenotype, higher psychosine levels in the rodent brainstem and spinal cord, and a significantly shorter life-span of the mice. Intriguingly, GALC expression peaks during this critical developmental period in mice. Further analysis of this mouse model reveals a cell autonomous role for GALC in the development and maturation of immature T-box-brain-1 positive brainstem neurons. These data identify a perinatal developmental period, in which neuronal GALC expression influences brainstem development that is critical for KD pathogenesis.

Pre-clinical Mouse Models of Neurodegenerative Lysosomal Storage Diseases

There are over 50 lysosomal hydrolase deficiencies, many of which cause neurodegeneration, cognitive decline and death. In recent years, a number of broad innovative therapies have been proposed and investigated for lysosomal storage diseases (LSDs), such as enzyme replacement, substrate reduction, pharmacologic chaperones, stem cell transplantation, and various forms of gene therapy. Murine models that accurately reflect the phenotypes observed in human LSDs are critical for the development, assessment and implementation of novel translational therapies. The goal of this review is to summarize the neurodegenerative murine LSD models available that recapitulate human disease, and the pre-clinical studies previously conducted. We also describe some limitations and difficulties in working with mouse models of neurodegenerative LSDs.

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.

Astrocyte morphogenesis is dependent on BDNF signaling via astrocytic TrkB.T1

Brain-derived neurotrophic factor (BDNF) is a critical growth factor involved in the maturation of the CNS, including neuronal morphology and synapse refinement. Herein, we demonstrate astrocytes express high levels of BDNF’s receptor, TrkB (in the top 20 of protein-coding transcripts), with nearly exclusive expression of the truncated isoform, TrkB.T1, which peaks in expression during astrocyte morphological maturation. Using a novel culture paradigm, we show that astrocyte morphological complexity is increased in the presence of BDNF and is dependent upon BDNF/TrkB.T1 signaling. Deletion of TrkB.T1, globally and astrocyte-specifically, in mice revealed morphologically immature astrocytes with significantly reduced volume, as well as dysregulated expression of perisynaptic genes associated with mature astrocyte function. Indicating a role for functional astrocyte maturation via BDNF/TrkB.T1 signaling, TrkB.T1 KO astrocytes do not support normal excitatory synaptogenesis or function. These data suggest a significant role for BDNF/TrkB.T1 signaling in astrocyte morphological maturation, a critical process for CNS development.

Suppression of galactocerebrosidase premature termination codon and rescue of galactocerebrosidase activity in twitcher cells

Krabbe's disease (KD) is a degenerative lysosomal storage disease resulting from deficiency of β-galactocerebrosidase activity. Over 100 mutations are known to cause the disease, and these usually occur in compound heterozygote patterns. In affected patients, nonsense mutations leading to a nonfunctional enzyme are often found associated with other mutations. The twitcher mouse is a naturally occurring model of KD, containing in β-galactocerebrosidase a premature stop codon, W339X. Recent studies have shown that selected compounds may induce the ribosomal bypass of premature stop codons without affecting the normal termination codons. The rescue of β-galactocerebrosidase activity induced by treatment with premature termination codon (PTC) 124, a well-characterized compound known to induce ribosomal read-through, was investigated on oligodendrocytes prepared from twitcher mice and on human fibroblasts from patients bearing nonsense mutations. The effectiveness of the nonsense-mediated mRNA decay (NMD) inhibitor 1 (NMDI1), a newly identified inhibitor of NMD, was also tested. Incubation of these cell lines with PTC124 and NMDI1 increased the levels of mRNA and rescued galactocerebrosidase enzymatic activity in a dose-dependent manner. The low but sustained expression of β-galactocerebrosidase in oligodendrocytes was sufficient to improve the morphology of the differentiated cells. Our in vitro approach provides the basis for further investigation of ribosomal read-through as an alternative therapeutic strategy to ameliorate the quality of life in selected KD patients. © 2016 Wiley Periodicals, Inc.

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.

Biochemical, cell biological, pathological, and therapeutic aspects of Krabbe's disease

Krabbe's disease (KD; also called globoid cell leukodystrophy) is a genetic disorder involving demyelination of the central (CNS) and peripheral (PNS) nervous systems. The disease may be subdivided into three types, an infantile form, which is the most common and severe; a juvenile form; and a rare adult form. KD is an autosomal recessive disorder caused by a deficiency of galactocerebrosidase activity in lysosomes, leading to accumulation of galactoceramide and neurotoxic galactosylsphingosine (psychosine [PSY]) in macrophages (globoid cells) as well as neural cells, especially in oligodendrocytes and Schwann cells. This ultimately results in damage to myelin in both CNS and PNS with associated morbidity and mortality. Accumulation of PSY, a lysolipid with detergent-like properties, over a threshold level could trigger membrane destabilization, leading to cell lysis. Moreover, subthreshold concentrations of PSY trigger cell signaling pathways that induce oxidative stress, mitochondrial dysfunction, apoptosis, inflammation, endothelial/vascular dysfunctions, and neuronal and axonal damage. From the time the "psychosine hypothesis" was proposed, considerable efforts have been made in search of an effective therapy for lowering PSY load with pharmacological, gene, and stem cell approaches to attenuate PSY-induced neurotoxicity. This Review focuses on the recent advances and prospective research for understanding disease mechanisms and therapeutic approaches for KD. © 2016 Wiley Periodicals, Inc.

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.

Delivering drugs to the central nervous system: an overview

Developing therapies for the brain is perhaps the greatest challenge facing modern medicine today. While a great many potential therapies show promise in animal models, precious few make it to approval or are even studied in human patients. The particular challenges to the translation of neurotherapeutics to the clinic are many, but a major barrier is difficulty in delivering therapeutics into the brain. The goal of this workshop was to present ways to deliver therapeutics to the brain, including the limitations of each method, and describe ways to track their delivery, safety, and efficacy. Solving the problem of delivery will aid translation of therapeutics for patients suffering from neurodegeneration and other disorders of the brain.

Experimental therapies in the murine model of globoid cell leukodystrophy

BACKGROUND

Globoid cell leukodystrophy or Krabbe disease, is a rapidly progressive childhood lysosomal storage disorder caused by a deficiency in galactocerebrosidase. Galactocerebrosidase deficiency leads to the accumulation of galactosylsphingosine (psychosine), a cytotoxic lipid especially damaging to oligodendrocytes and Schwann cells. The progressive loss of cells involved in myelination results in a dysmyelinating phenotype affecting both the central and peripheral nervous systems. Current treatment for globoid cell leukodystrophy is limited to bone marrow or umbilical cord blood transplantation. However, these therapies are not curative and simply slow the progression of the disease. The Twitcher mouse is a naturally occurring biochemically faithful model of human globoid cell leukodystrophy that has been used extensively to study globoid cell leukodystrophy pathophysiology and experimental treatments. In this review, we present the major single and combination experimental therapies targeting specific aspects of murine globoid cell leukodystrophy.

METHODS

Literature review and analysis.

RESULTS

The evidence suggests that even with the best available therapies, targeting a single pathogenic mechanism provides minimal clinical benefit. More recently, combination therapies have demonstrated the potential to further advance globoid cell leukodystrophy treatment by synergistically increasing life span. However, such therapies must be designed and evaluated carefully because not all combination therapies yield such positive results.

CONCLUSIONS

A more complete understanding of the underlying pathophysiology and the interplay between various therapies holds the key to the discovery of more effective treatments for globoid cell leukodystrophy.

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.

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.

Genetic evidence that brain-derived neurotrophic factor mediates competitive interactions between individual cortical neurons

Brain-derived neurotrophic factor (BDNF) is a secreted protein important for development and function of neocortical circuitry. Although it is well established that BDNF contributes to the sculpting of dendrite structure and modulation of synapse strength, the range and directionality of BDNF signaling underlying these functions are incompletely understood. To gain insights into the role of BDNF at the level of individual neurons, we tested the cell-autonomous requirements for Bdnf in visual cortical layer 2/3 neurons. We found that the number of functional Bdnf alleles a neuron carries relative to the prevailing genotype determines its density of dendritic spines, the structures at which most excitatory synapses are made. This requirement for Bdnf exists both during postnatal development and in adulthood, suggesting that the amount of BDNF a neuron is capable of producing determines its success in ongoing competition in the environment of the neocortex. Our results suggest that BDNF may perform a long-sought function for a secreted growth factor in mediating the competitive events that shape individual neurons and their circuits.

Psychosine induces the dephosphorylation of neurofilaments by deregulation of PP1 and PP2A phosphatases

Patients with Krabbe disease, a genetic demyelinating syndrome caused by deficiency of galactosyl-ceramidase and the resulting accumulation of galactosyl-sphingolipids, develop signs of a dying-back axonopathy compounded by a deficiency of large-caliber axons. Here, we show that axonal caliber in Twitcher mice, an animal model for Krabbe disease, is impaired in peripheral axons and is accompanied by a progressive reduction in the abundance and phosphorylation of the three neurofilament (NF) subunits. These changes correlate with an increase in the density of NFs per cross-sectional area in numerous mutant peripheral axons and abnormal increases in the activity of two serine/threonine phosphatases (PP1 and PP2A) in mutant tissue. Similarly, acutely isolated mutant cortical neurons show abnormal phosphorylation of NFs. Psychosine, the neurotoxin accumulated in Krabbe disease, was sufficient to induce abnormal dephosphorylation of NF subunits in a normal motor neuron cell line as well as in acutely isolated normal cortical neurons. This in vitro effect was mediated by PP1 and PP2A, which specifically dephosphorylated NFs. These results demonstrate that the reduced caliber observed in some axons in Krabbe disease involves abnormal dephosphorylation of NFs. We propose that a psychosine-driven pathogenic mechanism through deregulated phosphotransferase activities may be involved in this process.

Local siRNA delivery by non-viral vectors

Since the discovery of the RNA interference (RNAi) phenomenon, RNAi-based therapies now present a huge potential for the treatment of many diseases, including inflammatory and infectious diseases and cancers. While numerous reports have described the development of small interfering RNA (siRNA) delivery systems for in-vivo applications, only a small number of siRNA-based therapies are currently under clinical development. This is essentially due to the lack of efficient and safe siRNA delivery systems for intravenous administration. However, the delivery of siRNA after local injection could represent an attractive route of administration to limit the issues of toxicity associated with systemic injection. We will describe here the different synthetic vectors which have been developed for the local delivery of siRNA in various organs.

Effect of intrastriatal mesenchymal stromal cell injection on progression of a murine model of Krabbe disease

One of a family of devastating lysosomal storage disorders, Krabbe disease is characterized by demyelination, psychosine accumulation, and inflammation. Affected infants rarely survive longer than 2 years. Using the twitcher mouse model of the disease, this study evaluated the potential of intrastriatal injection of adipose or bone marrow-derived mesenchymal stromal cells (MSCs) as a treatment option. Neonatal pups were injected with MSCs at 3-4 days of age and subjected to a battery of behavioral tests beginning at 15 days. While MSC injection failed to increase lifespan of twitchers, improvements in rotarod performance and twitching severity were observed at 27-38 days of age using MSCs derived from bone marrow. This study tested several different tasks developed in adult mice for evaluation of disease progression in immature twitchers. Rotarod was both reliable and extremely sensitive. Automated gait analysis using the Treadscan program was also useful for early evaluation of differences prior to overt gait dysfunction. Finally, this study represents the first use of the Stone T-maze in immature mice. Validation of rotarod and automated gait analysis for detection of subtle differences in disease progression is important for early stage efforts to develop treatments for juvenile disorders.

CNS-targeted AAV5 gene transfer results in global dispersal of vector and prevention of morphological and function deterioration in CNS of globoid cell leukodystrophy mouse model

Globoid cell leukodystrophy (GLD) is a devastating lysosomal storage disease caused by deficiency of the enzyme galactocerebrosidase (GALC). Currently, there is no definite cure for GLD. Several attempts with CNS-directed gene therapy in twitcher mice (a murine model of GLD) demonstrated restricted expression of GALC activity in CNS and failure of therapeutic efficacy in cerebellum and spinal cord, resulting in various degrees of correction of biochemical, pathological and clinical phenotype. More recently, twitcher mice receiving a combination of hematopoietic and viral vector gene transfer therapies were not protected from neurodegeneration and axonopathy in both cerebellum and spinal cord. This evidence indicates the requirement of sufficient and widespread GALC expression in CNS and rescue of cerebellum and spinal cord in the therapeutic intervention of murine model of GLD. In this study, we have optimized intracranial delivery of AAV2/5-GALC to the neocortex, hippocampus and cerebellum, instead of the thalamus as was previously conducted, of twitcher mice. The CNS-targeted AAV2/5 gene transfer effectively dispersed GALC transgene along the neuraxis of CNS as far as the lumbar spinal cord, and reduced the accumulation of psychosine in the CNS of twitcher mice. Most importantly, the treated twitcher mice were protected from loss of oligodendrocytes and Purkinje cells, axonopathy and marked gliosis, and had significantly improved neuromotor function and prolonged lifespan. These preclinical findings with our approach are encouraging, although a more robust response in the spinal cord would be desirable. Collectively, the information in this study validates the efficacy of this gene delivery approach to correct enzymatic deficiency, psychosine accumulation and neuropathy in CNS of GLD. Combining cell therapy such as bone marrow transplantation with treatment with the aim of reducing inflammation, replacing dead or dying oligodendrocytes and targeting PNS may provide a synergistic and more complete correction of this disease.

Mesenchymal lineage stem cells have pronounced anti-inflammatory effects in the twitcher mouse model of Krabbe's disease

The twitcher mouse is an animal model of Krabbe's disease (KD), which is a neurodegenerative lysosomal storage disorder resulting from the absence of functional lysosomal enzyme galactocerebrosidase (GALC). This disease affects the central and peripheral nervous systems and in its most severe form results in death before the age of 2 in humans and approximately 30-40 days in mice. This study evaluates the effect of intracerebroventricular administration of mesenchymal stem cells derived from adipose tissue (ASCs) and bone marrow (BMSCs) on the pathology of KD. Subsequent to the intracerebroventricular injection of ASCs or BMSCs on postnatal day (PND) 3-4, body weight, lifespan, and neuromotor function were evaluated longitudinally beginning on PND15. At sacrifice, tissues were harvested for analysis of GALC activity, presence of myelin, infiltration of macrophages, microglial activation, inflammatory markers, and cellular persistence. Survival analysis curves indicate a statistically significant increase in lifespan in stem cell-treated twitcher mice as compared with control twitcher mice. Body weight and motor function were also improved compared with controls. The stem cells may mediate some of these benefits through an anti-inflammatory mechanism because the expression of numerous proinflammatory markers was downregulated at both transcriptional and translational levels. A marked decrease in the levels of macrophage infiltration and microglial activation was also noted. These data indicate that mesenchymal lineage stem cells are potent inhibitors of inflammation associated with KD progression and offer potential benefits as a component of a combination approach for in vivo treatment by reducing the levels of inflammation.

Short-term rescue of neonatal lethality in a mouse model of propionic acidemia by gene therapy

Propionic acidemia (PA) is a metabolic disorder that causes mental retardation and that can be fatal if untreated. PA is inherited in an autosomal recessive fashion involving mutations in PCCA or PCCB encoding the alpha and beta subunits of propionyl-CoA carboxylase (PCC). Current treatment is based on dietary restriction of substrate amino acids, which attenuates symptoms. However, patients still experience episodes of hyperammonemia that can cause progressive neurologic damage. In this paper, we have tested gene therapy approaches to PA in a stringent mouse model of PCCA deficiency, in which homozygous knockout mice are born but die within 36 hr. In this work, we have delivered first-generation and helper-dependent adenovirus serotype 5 (Ad5) vectors expressing the human PCCA cDNA by intraperitoneal injection into newborn mice. Unmodified Ad5 vectors mediated extensive transduction of the peritoneum with weak liver transduction as determined by luciferase imaging and dsRed expression. In contrast, modification of Ad5 with polyethylene glycol detargeted the virus from the peritoneum and retargeted it for transduction in the liver. When vectors expressing PCCA were injected, significant increases in life span were observed for both the unmodified and polyethylene glycol (PEG)-modified Ad5 vectors. However, this rescue was transient. Similarly, adeno-associated virus serotype 8-mediated transduction also produced only transient rescue. These data show first proof of principle for gene therapy of PA and demonstrate the potential utility of PEG to modify viral tropism in an actual gene therapy application.

Widespread enzymatic correction of CNS tissues by a single intracerebral injection of therapeutic lentiviral vector in leukodystrophy mouse models

Leukodystrophies are rare diseases caused by defects in the genes coding for lysosomal enzymes that degrade several glycosphingolipids. Gene therapy for leukodystrophies requires efficient distribution of the missing enzymes in CNS tissues to prevent demyelination and neurodegeneration. In this work, we targeted the external capsule (EC), a white matter region enriched in neuronal projections, with the aim of obtaining maximal protein distribution from a single injection site. We used bidirectional (bd) lentiviral vectors (LV) (bdLV) to ensure coordinate expression of a therapeutic gene (beta-galactocerebrosidase, GALC; arylsulfatase A, ARSA) and of a reporter gene, thus monitoring simultaneously transgene distribution and enzyme reconstitution. A single EC injection of bdLV.GALC in early symptomatic twitcher mice (a murine model of globoid cell leukodystrophy) resulted in rapid and robust expression of a functional GALC protein in the telencephalon, cerebellum, brainstem and spinal cord. This led to global rescue of enzymatic activity, significant reduction of tissue storage and decrease of activated astroglia and microglia. Widespread protein distribution and complete metabolic correction were also observed after EC injection of bdLV.ARSA in a mouse model of metachromatic leukodystrophy. Our data indicated axonal transport, distribution through cerebrospinal fluid flow and cross-correction as the mechanisms contributing to widespread bioavailability of GALC and ARSA proteins in CNS tissues. LV-mediated gene delivery of lysosomal enzymes by targeting highly interconnected CNS regions is a potentially effective strategy that, combined with a treatment able to target the PNS and peripheral organs, may provide significant therapeutic benefit to patients affected by leukodystrophies.

Intracerebral cell transplantation therapy for murine GM1 gangliosidosis

We performed a cell transplantation study to treat the brain involvement in lysosomal storage diseases. We used acid beta-galactosidase knock-out mice (BKO) from C57BL/6 as recipients. To minimize immune responses, we used cells derived from transgenic mice of C57BL/6 overexpressing the normal human beta-galactosidase. Fetal brain cells (FBC), bone marrow-derived mesenchymal stem cells (MSC), and mixed FBC and MSC cells were prepared and injected into the ventricle of newborn BKO mouse brain. The mice were examined at 1, 2, 4, and 8 weeks and 6 months after injection. In each experiment, the injected cells migrated into the whole brain effectively and survived for at least 8 weeks. Decrease in ganglioside GM1 level was also observed. FBC could survive for 6 months in recipient brain. However, the number of transplanted FBC decreased. In the brains of MSC- or mixed cell-treated mice, no grafted cells could be found at 6 months. To achieve sufficient long-term effects on the brain, a method of steering the immune response away from cytotoxic responses or of inducing tolerance to the products of therapeutic genes must be developed.

Large animal models of neurological disorders for gene therapy

he development of therapeutic interventions for genetic disorders and diseases that affect the central nervous system (CNS) has proven challenging. There has been significant progress in the development of gene therapy strategies in murine models of human disease, but gene therapy outcomes in these models do not always translate to the human setting. Therefore, large animal models are crucial to the development of diagnostics, treatments, and eventual cures for debilitating neurological disorders. This review focuses on the description of large animal models of neurological diseases such as lysosomal storage diseases, Parkinsons disease, Huntingtons disease, and neuroAIDS. The review also describes the contributions of these models to progress in gene therapy research.

Significant correction of pathology in brains of twitcher mice following injection of genetically modified mouse neural progenitor cells

Krabbe disease or globoid cell leukodystrophy is an autosomal recessive disorder resulting from mutations in the galactocerebrosidase (GALC) gene. These mutations lead to deficient GALC activity, storage of substrates of the enzyme, including psychosine, death to oligodendrocytes, decreased myelination, production of globoid cells and eventually death to the individual. While most affected individuals are infants, late-onset forms are also recognized. In addition to human patients, several animal models have been well characterized, including the twitcher mouse. A spontaneously transformed progenitor cell line was isolated from an astrocyte-enriched fraction of normal mice, partially characterized and transduced with a retrovirus-containing mouse GALC cDNA to produce increased GALC activity (20-30-fold above baseline). These cells, called MAR-52, were injected into the brains of newborn affected twitcher mice. While there was only a modest increase in lifespan and body weight, there was clear evidence for the correction of the astrocytic gliosis, normal appearing oligodendrocytes and evidence for remyelination. We demonstrate that the exogenously supplied neural progenitor cells can donate GALC enzyme to oligodendrocytes in the brains of affected mice resulting in normal myelination in the area of donor cells. At this time, hematopoietic stem cell transplantation provides the best outcome in affected mice and is the only treatment available for human patients, but it does not result in a cure even when performed in asymptomatic newborns. Complete correction probably will require a combined approach to effectively treat patients with Krabbe disease. With developments in the isolation and characterization of stem cells, this approach may improve the outcome for individuals diagnosed in the future.

Survival advantage of neonatal CNS gene transfer for late infantile neuronal ceroid lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis (LINCL), a fatal autosomal recessive neurodegenerative lysosomal storage disorder of childhood, is caused by mutations in the CLN2 gene, resulting in deficiency of the protein tripeptidyl peptidase I (TPP-I). We have previously shown that direct CNS administration of AAVrh.10hCLN2 to adult CLN2 knockout mice, a serotype rh.10 adeno-associated virus expressing the wild-type CLN2 cDNA, will partially improve neurological function and survival. In this study, we explore the hypothesis that administration of AAVrh.10hCLN2 to the neonatal brain will significantly improve the results of AAVrh.10hCLN2 therapy. To assess this concept, AAVrh.10hCLN2 vector was administered directly to the CNS of CLN2 knockout mice at 2 days, 3 wk and 7 wk of age. While all treatment groups show a marked increase in total TPP-I activity over wild-type mice, neonatally treated mice displayed high levels of TPP-I activity in the CNS 1 yr after administration which was spread throughout the brain. Using behavioral markers, 2 day-treated mice demonstrate marked improvement over 3 wk, 7 wk or untreated mice. Finally, neonatal administration of AAVrh.10hCLN2 was associated with markedly enhanced survival, with a median time of death 376 days for neonatal treated mice, 277 days for 3 wk-treated mice, 168 days for 7 wk-treated mice, and 121 days for untreated mice. These data suggest that neonatal treatment offers many unique advantages, and that early detection and treatment may be essential for maximal gene therapy for childhood lysosomal storage disorders affecting the CNS.

CNS-directed gene therapy for lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders usually caused by deficient activity of a single lysosomal enzyme. As most lysosomal enzymes are ubiquitously expressed, a deficiency in a single enzyme can affect multiple organ systems, including the central nervous system (CNS). At least 75% of all LSDs have a significant CNS component. Approaches such as bone marrow transplantation (BMT) or enzyme replacement therapy (ERT) can effectively treat the systemic disease associated with LSDs in some patients. However, CNS disease remains a major challenge. Gene therapy represents a promising approach for the treatment of CNS disease as it has the potential to provide a permanent source of the deficient enzyme. Direct intracranial injection of viral gene transfer vectors has resulted in reduced lysosomal storage and functional improvement in certain small (rodent) and large (canine and feline) animal models of LSDs. The addition of protein transduction domains (PTDs) to the recombinant enzymes increased the distribution of enzyme and the extent of correction. Therapeutic levels of lysosomal enzymes can also be delivered to distant sites in the brain by anterograde and retrograde axonal transport. Finally, combining disparate approaches such as BMT and CNS-directed gene therapy can increase treatment efficacy in LSDs with severe CNS disease that are refractory to more conventional approaches.

CONCLUSION

The development of gene transfer vectors that mediate persistent expression in vivo, the addition of PTDs, a better understanding of lysosomal enzyme trafficking and combining different therapies provide hope that the CNS component of LSDs can be effectively treated.

Comparison of the Behavior of Neural Stem Cells in the Brain of Normal and twitcher Mice after Neonatal Transplantation

The twitcher mouse is a model of human Krabbe's disease caused by a mutation in the galacto-cerebrosidase gene. As a result of deficient catabolism of myelin, death of oligodendrocytes and demyelination occur widely in the central and peripheral nervous system, making it an ideal model for investigation of myelin repair strategies. Here we describe the use of mouse neural stem cells (NSCs) expressing enhanced green fluorescence protein (eGFP) for transplantation in neonatal normal and twitcher mice. Normal and twitcher mice in all age groups (20, 30, and 45 days old) showed engraftment and differentiation of injected cells. The engrafted cells were found in the ventricles and a wide range of regions in the brain parenchyma. There was no significant difference in the total number of cells engrafted and the pattern of engraftment between 30-day-old normal and twitcher mice. The average number of engrafted cells in the brain of a 30-day-old mouse was 964 +/- 281 (n = 8). Engrafted cells with the morphology of neurons, astrocytes, and oligodendrocytes were identified. Differentiation into oligodendrocytes was confirmed by immunohistochemical staining using a cell-type-specific marker. There was a higher percentage of cells engrafted in the grey matter than in the white matter (p < 0.01) in both normal and twitcher mouse brain. This study indicates that the environment of demyelination in 30-day-old twitcher mouse brain has not significantly altered the engraftment and distribution patterns of NSCs after neonatal transplantation.

Molecular beacon genotyping for globoid cell leukodystrophy from hair roots in the twitcher mouse and rhesus macaque

Rapid and accurate genotype determination is ideal for the maintenance of breeding colonies of laboratory animal models of genetic disease. The rhesus macaque and murine (twitcher) models of globoid cell leukodystrophy have a dinucleotide deletion or single nucleotide substitution, respectively, which abolish ceramide beta-galactosidase activity and are authentic models of Krabbe disease. We report a molecular beacon PCR assay for each species which allows unambiguous determination of the genotype in under 4h. The assay works reliably with DNA extracted from hair roots using Chelex-100 in a 20 min, 100 degrees C incubation. We demonstrate that genotyping from hair roots is a preferred alternative to collecting blood or tissue for DNA extraction because it reduces animal distress, uses an inexpensive reagent, and is simpler and faster. Following amplification on a standard thermocycler with a 96-well plate format, these molecular beacon assays can be read on a standard laboratory fluorescent plate reader, eliminating the need to use a real-time thermocycler or to open the plate for subsequent restriction enzyme digestion and gel electrophoresis. The multiplexed ratio of fluorescence from wild-type- and mutant-specific beacons reporting at 560 nm and 535 nm wavelengths is distinct for each genotype.

Central Nervous System-directed AAV2/5-Mediated Gene Therapy Synergizes with Bone Marrow Transplantation in the Murine Model of Globoid-cell Leukodystrophy

Globoid-cell leukodystrophy (GLD) is a rapidly progressing inherited neurodegenerative disorder caused by a deficiency in galactosylceramidase activity. Previous studies in the murine model of GLD (Twitcher mouse) have shown that both bone marrow transplantation (BMT) and central nervous system (CNS)-directed gene therapy can be moderately effective at ameliorating certain aspects of GLD. As BMT and CNS-directed gene therapy target fundamentally different tissues, we tested the hypothesis that combining these disparate therapies would be more efficacious than either therapy alone. Mice receiving myeloreductive conditioning at birth followed by syngeneic BMT had approximately 25-35% donor chimerism. Untreated Twitcher mice, Twitcher mice treated with BMT alone, AAV2/5 alone, or a combination of BMT and AAV2/5 had mean lifespans of 39, 44, 49, and 104 days, respectively. Twitcher mice treated with a combination of BMT and AAV2/5 also had significantly improved performance in several behavioral tests and greater reduction in demyelination, astrocytosis, and macrophage infiltration compared to untreated Twitcher mice or mice that received either therapy alone. These data suggest that CNS-directed gene therapy synergizes with BMT. The combination of these disparate therapeutic approaches may form the basis for more effective treatment of this inherited neurodegenerative disorder.

Design and optimization of lentiviral vectors for transfer of GALC expression in Twitcher brain

BACKGROUND

Demyelination in globoid cell leukodystrophy (GLD) is due to a deficiency of galactocerebrosidase (GALC) activity. Up to now, in vivo brain viral gene transfer of GALC showed modest impact on disease development in Twitcher mice, an animal model for GLD. Lentiviral vectors, which are highly efficient to transfer the expression of therapeutic genes in neurons and glial cells, have not been evaluated for direct cerebral therapy in GLD mice.

METHODS

Lentiviral vectors containing the untagged cDNA or the hemagglutinin (HA)-tagged cDNA for the full-length mouse GALC sequence were generated and validated in vitro. In vivo therapeutic efficacy of these vectors was evaluated by histology, biochemistry and electrophysiology after transduction of ependymal or subependymal layers in young Twitcher pups.

RESULTS

Both GALC lentiviral vectors transduced neurons, oligodendrocytes and astrocytes with efficiencies above 75% and conferred high levels of enzyme activity. GALC accumulated in lysosomes of transduced cells and was also secreted to the extracellular medium. Conditioned GALC medium was able to correct the enzyme deficiency when added to non-transduced Twitcher glial cultures. Mice that received intraventricular injections of GALC vector showed accumulation of GALC in ependymal cells but no diffusion of the enzyme from the ependymal ventricular tree into the cerebral parenchyma. Significant expression of GALC-HA was detected in neuroglioblasts when GALC-HA lentiviral vectors were injected in the subventricular zone of Twitcher mice. Life span and motor conduction in both groups of treated Twitcher mice were not significantly ameliorated.

CONCLUSIONS

Lentiviral vectors showed to be efficient for reconstitution of the GALC expression in Twitcher neural cells. GALC was able to accumulate in lysosomes as well as to enter the secretory pathway of lysosomal enzymes, two fundamental aspects for gene therapy of lysosomal storage diseases. Our in vivo results, while showing the capacity of lentiviral vectors to transfer expression of therapeutic GALC in the Twitcher brain, did not limit progression of disease in Twitchers and highlight the need to evaluate other routes of administration.

Suppression of galactosylceramidase (GALC) expression in the twitcher mouse model of globoid cell leukodystrophy (GLD) is caused by nonsense-mediated mRNA decay (NMD)

The twitcher mouse is a pathologically and enzymatically authentic model of globoid cell leukodystrophy (GLD, Krabbe disease) that has been widely used for the evaluation of potential therapeutic approaches. This naturally occurring mouse model contains a premature stop codon (W339X) in the galactosylceramidase (GALC) gene that abolishes enzymatic activity. Using either immunocytochemical approaches or Western blot methodology, we have been unable to detect the truncated form of GALC expected to be produced in these animals. Nonsense-mediated mRNA decay (NMD) is a cellular protection mechanism that degrades newly synthesized transcripts containing a premature termination codon (PTC). Since the naturally occurring mutation in the twitcher mouse introduces a PTC, we hypothesized that NMD might affect the degradation of GALC mRNA in these animals. Consistent with this hypothesis, we determined that the amount of GALC transcript was inversely proportional to the number of twitcher containing alleles. Similar reductions in GALC mRNA were detected in a twitcher-derived Schwann cell line (TwS1) when compared to wild-type Schwann cells (IMS32). Anisomycin, emetine and puromycin, inhibitors of NMD, effectively increased the level of GALC transcript in the TwS1 cells providing further support for nonsense-mediated mRNA decay being the mechanism by which no GALC protein is detected in these animals. Understanding the mechanistic differences between the lack of enzymatic activity in the twitcher model and that observed with the missense mutations that cause human disease yields not only novel therapeutic insights but also highlights the need for additional animal models.

Gene therapy for lysosomal storage diseases

Lysosomal storage diseases (LSDs) comprise a diverse group of monogenetic disorders with complex clinical phenotypes that include both systemic and central nervous system pathologies. In recent years, the identification or development of mouse models recapitulating the clinical course of the LSDs has been instrumental in evaluating therapeutic strategies. Here, we review the various gene replacement strategies for target organs affected in many LSDs and describe briefly the various vector systems employed to test how best to accomplish long-lasting therapies for these fatal disorders.

The therapeutic potential of neural stem/progenitor cells in murine globoid cell leukodystrophy is conditioned by macrophage/microglia activation

Twitcher (GALC(twi/twi)) is the murine model of globoid cell leukodystrophy (GLD or Krabbe disease), a disease caused by mutations of the lysosomal enzyme galactocerebrosidase (GALC). To verify the therapeutic potential on twitcher of neural stem/progenitor cells (NSPC), we transduced them with a GALC lentiviral vector. Brain injection of NSPC-GALC increased survival of GALC(twi/twi) from 36.1 +/- 4.1 to 52.2 +/- 5.6 days (P < 0.0001). Detection of GALC activity and flow cytometry showed that NSPC-GALC and NSPC expressing the green fluorescent protein were attracted to the posterior area of twitcher brain, where demyelination occurs first. GALC(twi/twi) microglia, also more abundant in posterior regions of the brain, released significant amounts of the cytotoxic cytokine TNF-alpha when matched with NSPC-GALC. Thus, in murine GLD, and possibly in other demyelinating diseases, NSPC are attracted to regions of active demyelination but have limited survival and therapeutic potential if attacked by activated macrophages/microglia.

Widespread gene transduction to the central nervous system by adenovirus in utero: implication for prenatal gene therapy to brain involvement of lysosomal storage disease

BACKGROUND

In some lysosomal storage diseases, considerable alterations of the central nervous system (CNS) occur prior to birth and neurodegeneration progresses rapidly soon after birth causing early death in patients. No effective treatment is available after birth. Treatment may need to be initiated before birth to prevent the onset or progression of neurological changes and thereby irreversible brain damage. The aim of this study is to investigate the feasibility and effectiveness of brain-directed prenatal gene therapy for lysosomal storage diseases.

METHODS

Recombinant adenovirus encoding the lacZ gene was injected into the lateral ventricles of mouse embryos and the pattern of gene transduction to the CNS was investigated. In the therapeutic experiment, adenovirus expressing beta-glucuronidase was injected into the cerebral ventricles of the embryos of mucopolysaccharidosis VII mice and the therapeutic effects on the brain were evaluated.

RESULTS

Injection of adenoviral vectors to the cerebral ventricles of mouse embryos led to widespread gene transduction throughout the brain and the spinal cord and transgene expression persisted over 10 months in those surviving the procedure. The prenatal transduction of the therapeutic gene to the brain of the mucopolysaccharidosis VII mouse efficiently prevented lysosomal storage in most brain cells before birth until 4 months after birth.

CONCLUSIONS

Brain-directed in utero gene therapy through an intra-ventricular route would be an effective strategy to treat some lysosomal storage diseases with early and severe CNS alterations.

AAV2/5 vector expressing galactocerebrosidase ameliorates CNS disease in the murine model of globoid-cell leukodystrophy more efficiently than AAV2

Globoid-cell leukodystrophy (GLD) is an autosomal recessive lysosomal storage disorder caused by mutations in the galactosylceramidase (GALC) gene. Infantile GLD has a lethal course with severe cerebral demyelination that progresses to death by 2 years of age. In the current study twitcher mice, an authentic murine model of infantile GLD, were given intracranial injections of either recombinant adeno-associated virus serotype 2 encoding the murine Galc cDNA (AAV2-GALC) or the same genome pseudotyped with AAV5 capsid proteins (AAV2/5-GALC) on day 3 of age. The group injected intracranially with AAV2/5-GALC had approximately 25-fold greater than normal Galc levels in the brain, while AAV2-GALC-injected animals had 28% normal levels. The average life expectancy of twitcher mice ( approximately 38 days) was significantly (P < 0.0001) increased to 48 and 52 days for the AAV2-GALC- and AAV2/5-GALC-treated groups, respectively. The AAV2/5-GALC group performed significantly better in a battery of behavioral tests compared to untreated, AAV2-GFP-treated, or AAV2-treated twitcher animals. This longitudinal study demonstrated that AAV2/5-GALC-mediated gene therapy resulted in higher levels of Galc expression and slowed the neurologic deterioration more completely than AAV2-GALC in the murine model of globoid-cell leukodystrophy. However, the clinical improvements, as assessed by behavioral tests and life span, were only modest.

Clinico-pathological rescue of a model mouse of Huntington's disease by siRNA

Huntington's disease (HD) is an autosomal dominant inheritable neurodegenerative disorder currently without effective treatment. It is caused by an expanded polyglutamine (poly Q) tract in the corresponding protein, huntingtin (htt), and therefore suppressing the huntingtin expression in brain neurons is expected to delay the onset and mitigate the severity of the disease. Here, we have used small interfering RNAs (siRNAs) directed against the huntingtin gene to repress the transgenic mutant huntingtin expression in an HD mouse model, R6/2. Results showed that intraventricular injection of siRNAs at an early postnatal period inhibited transgenic huntingtin expression in brain neurons and induced a decrease in the numbers and sizes of intranuclear inclusions in striatal neurons. Treatments using this siRNA significantly prolonged model mice longevity, improved motor function and slowed down the loss of body weight. This work suggests that siRNA-based therapy is promising as a future treatment for HD.

Hematopoietic Cell Transplantation Ameliorates Clinical Phenotype and Progression of the CNS Pathology in the Mouse Model of Late Onset Krabbe Disease

Krabbe disease is a genetic demyelinating disease caused by a deficiency of galactosylceramidase. The majority of cases are of infantile onset with rapid clinical course. A rare late onset form with milder clinical symptoms also exists. The latter form has been reported to respond well to the bone marrow transplantation (BMT) therapy. We tested whether the BMT could be an effective therapy for the mouse model of the late onset form, saposin-A-/- (SAP-A-/-) mice. We used green fluorescent protein transgenic mice as the donors. Chimeric SAP-A-/- mice that received BMT showed very little evidence of neurologic symptoms. At postnatal day 190 when severe demyelination was evident in naive SAP-A-/- mice, demyelination was virtually absent in the brain of chimeric SAP-A-/- mice. Presence of residual enzyme activity, at the time of rapid myelination in SAP-A-/- mice, appears to limit initial inflammatory responses and macrophage infiltration, thereby preventing progression of demyelination in the CNS in SAP-A-/- mice. In contrast, the peripheral nerves showed features of hypertrophic neuropathy with hypomyelination and onion bulb formation, suggesting that there are different cellular responses to the BMT in the CNS and PNS.

Enzyme replacement therapy results in substantial improvements in early clinical phenotype in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) or Krabbe disease is a devastating, degenerative neurological disorder caused by mutations in the galactosylceramidase (GALC) gene that severely affect enzyme activity. Currently, treatment options for this disorder are very limited. Enzyme replacement therapy (ERT) has been shown to be effective in lysosomal storage disorders with predominantly peripheral manifestations such as type I Gaucher's and Fabry's disease. Little however is known about the possible benefit of ERT in GLD, which has a substantial central nervous system component. In this study, we examined the effect of peripheral GALC injections in the twitcher mouse model of the disease. Although we were unable to block the precipitous decline that normally occurs just before death, we did observe significant early improvements in motor performance, a substantial attenuation in the initial failure to thrive, and an increase in life span. Immunohistochemical and activity analyses demonstrated GALC uptake in multiple tissues, including the brain. This was associated with a decrease in the abnormal accumulation of the GALC substrate psychosine, which is thought to play a pivotal role in disease pathology. These results indicate that peripheral ERT is likely to be beneficial in GLD.

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

Globoid cell leukodystrophy (GLD) or Krabbe disease is a neurodegenerative disorder caused by a deficiency of galactocerebrosidase (GALC) activity. GALC is required for the lysosomal degradation of galactosylceramide, psychosine, and possibly other galactolipids. This process is extremely important during active myelination. In the absence of functional GALC, psychosine accumulates, resulting in the apoptotic death of myelin-producing cells. While most patients are infants who do not survive beyond 2 years of age, some older patients are also diagnosed. Hematopoietic stem cell transplantation has proven to have a positive effect on the course of some patients with late-onset Krabbe disease. Murine models of this disease provide an excellent opportunity to evaluate therapeutic alternatives including gene therapy. In this study we used serotype 1 AAV to express mouse GALC under the control of the human cytomegalovirus promoter. Direct administration of these viral particles into the brains of neonatal mice with GLD resulted in sustained expression of GALC activity, improved myelination, attenuated symptoms, and prolonged life span. While this treatment also resulted in significant pathological improvements, the treated mice died with symptoms similar to those of the untreated mice. Additional initiatives may be required to prevent the onset of disease and reverse the course of the disease in animal models and human patients.

GALC transduction leads to morphological improvement of the twitcher oligodendrocytes in vivo

Globoid cell leukodystrophy (GLD, Krabbe disease) is a severe demyelinating disease caused by a genetic defect of beta-galactocerebrosidase (GALC). To date treatment to GLD is limited to hematopoietic stem cell transplantation. Experimental approaches by means of gene therapy in twitcher mouse, an authentic murine model of human GLD, showed significant but only marginal improvements of the disease. To clarify whether the introduction of GALC could provide beneficial effects on the oligodendrocytes in GLD, we transduced twitcher oligodendrocytes by stereotactically injecting recombinant retrovirus encoding GALC-myc-tag fusion gene into the forebrain subventricular zone of neonatal twitcher mouse. In vivo effects of exogenous GALC on twitcher oligodendrocytes were studied histologically by combined immunostaining for the myc-epitope and the oligodendroglial specific marker, pi form of glutathione-S-transferase, at around 40 days of age. We show here that GALC transduction led to dramatic morphological improvement of the twitcher oligodendrocytes comparing with those in untreated twitcher controls. This study provided direct in vivo evidence that GALC transduction could prevent or correct aberrant morphology of oligodendrocytes in GLD which may be closely related to the dysfunction and/or degeneration of oligodendrocytes and the demyelination in this disease.

Widespread and highly persistent gene transfer to the CNS by retrovirus vectorin utero: implication for gene therapy to Krabbe disease

BACKGROUND

Brain-directed prenatal gene therapy may benefit some lysosomal storage diseases that affect the central nervous system (CNS) before birth. Our previous study showed that intrauterine introduction of recombinant adenoviruses into cerebral ventricles results in efficient gene transfer to the CNS in the mouse. However, transgene expression decreased with time due to the non-integrative property of adenoviral vectors. In this study, in order to obtain permanent gene transduction, we investigated the feasibility of retrovirus-mediated in utero gene transduction.

METHODS

Concentrated retrovirus encoding the LacZ gene was injected into the cerebral ventricles of the embryos of normal and twitcher mice (a murine model of Krabbe disease) at embryonic day 12. The distribution and maintenance of the transgene expression in the recipient brain were analyzed histochemically, biochemically and by the quantitative polymerase chain reaction method pre- and postnatally.

RESULTS

Efficient and highly persistent gene transduction to the brain was achieved both in normal and the twitcher mouse. Transduced neurons, astrocytes and oligodendrocytes were distributed throughout the brain. The transduced LacZ gene, its transcript and protein expression in the brain were maintained for 14 months without decrement. In addition, gene transduction to multiple tissues other than the brain was also detected at low levels.

CONCLUSIONS

This study suggests that brain-directed in utero gene transfer using retrovirus vector may be beneficial to the treatment of lysosomal storage diseases with severe brain damage early in life, such as Krabbe disease.

Brain transplantation of genetically modified bone marrow stromal cells corrects CNS pathology and cognitive function in MPS VII mice

Current therapies for lysosomal storage diseases (LSDs), enzyme replacement therapy and bone marrow transplantation are effective for visceral organ pathology of LSD, but their effectiveness for brain involvement in LSDs is still a subject of controversy. As an alternative approach, we transplanted genetically modified bone marrow stromal (BMS) cells to lateral ventricle of newborn mucopolysaccharidosis VII (MPS VII) mice. MPS VII is one of LSDs and caused by deficiency of beta-glucuronidase (GUSB), resulting in accumulation of glycosaminoglycans (GAGs) in brain. At 2 weeks after transplantation, the GUSB enzyme-positive cells were identified in olfactory bulb, striatum and cerebral cortex, and the enzymatic activities in various brain areas increased. The GAGs contents in brain were reduced to near normal level at 4 weeks after transplantation. Although GUSB activity declined to homozygous level after 8 weeks, the reduction of GAGs persisted for 16 weeks. Microscopic examination indicated that the lysosomal distention was not found in treated animal brain. Cognitive function in MPS VII animals as evaluated by Morris Water Maze test in treated mice showed a marked improvement over nontreated animals. Brain transplantation of genetically modified BMS cells appears to be a promising approach to treat diffuse CNS involvement of LSDs.

Transgenic rescue of Krabbe disease in the twitcher mouse

The twitcher mouse is a natural model of Krabbe disease caused by galactocerebrosidase (GALC) deficiency. Previous attempts at rescuing the twitcher mouse by bone marrow transplantion, viral transduction, or transgenesis were only partially successful. Here, we report the transgenic (tg) rescue of the twitcher mouse with a BAC clone harboring the entire GALC. The twi/twi/hGALC tg mice exhibited growth, motor function, and fertility similar to those of nonaffected animals. These animals had normal levels of GALC activity in brain and were free of the typical twitcher demyelinating pathology. Surprisingly, GALC expression in twi/twi hGALC tg kidneys was low and galactocerebroside storage was only partially cleared. Nonetheless, these mice have been maintained for over 1 year without any sign of disease. Since pathological damage associated with GALC deficiency is confined to the nervous system, our work represents the first successful rescue of the twitcher mouse and opens the possibility of developing novel therapeutic approaches.