CD8+ T cell depletion prevents neuropathology in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) or Krabbe's disease is a fatal genetic demyelinating disease of the central nervous system caused by loss-of-function mutations in the galactosylceramidase (galc) gene. While the metabolic basis for disease is known, the understanding of how this results in neuropathology is not well understood. Herein, we report that the rapid and protracted elevation of CD8+ cytotoxic T lymphocytes occurs coincident with clinical disease in a mouse model of GLD. Administration of a function-blocking antibody against CD8α effectively prevented disease onset, reduced morbidity and mortality, and prevented CNS demyelination in mice. These data indicate that subsequent to the genetic cause of disease, neuropathology is driven by pathogenic CD8+ T cells, thus offering novel therapeutic potential for treatment of GLD.

Hyperglycemia increases SCO-spondin and Wnt5a secretion into the cerebrospinal fluid to regulate ependymal cell beating and glucose sensing

Hyperglycemia increases glucose concentrations in the cerebrospinal fluid (CSF), activating glucose-sensing mechanisms and feeding behavior in the hypothalamus. Here, we discuss how hyperglycemia temporarily modifies ependymal cell ciliary beating to increase hypothalamic glucose sensing. A high level of glucose in the rat CSF stimulates glucose transporter 2 (GLUT2)-positive subcommissural organ (SCO) cells to release SCO-spondin into the dorsal third ventricle. Genetic inactivation of mice GLUT2 decreases hyperglycemia-induced SCO-spondin secretion. In addition, SCO cells secrete Wnt5a-positive vesicles; thus, Wnt5a and SCO-spondin are found at the apex of dorsal ependymal cilia to regulate ciliary beating. Frizzled-2 and ROR2 receptors, as well as specific proteoglycans, such as glypican/testican (essential for the interaction of Wnt5a with its receptors) and Cx43 coupling, were also analyzed in ependymal cells. Finally, we propose that the SCO-spondin/Wnt5a/Frizzled-2/Cx43 axis in ependymal cells regulates ciliary beating, a cyclic and adaptive signaling mechanism to control glucose sensing.

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.

Tumor-targeting cell-penetrating peptide, p28, for glioblastoma imaging and therapy

Despite recent advances in cancer research, glioblastoma multiforme (GBM) remains a highly aggressive brain tumor as its treatment options are limited. The current standard treatment includes surgery followed by radiotherapy and adjuvant chemotherapy. However, surgery without image guidance is often challenging to achieve maximal safe resection as it is difficult to precisely discern the lesion to be removed from surrounding brain tissue. In addition, the efficacy of adjuvant chemotherapy is limited by poor penetration of therapeutics through the blood-brain barrier (BBB) into brain tissues, and the lack of tumor targeting. In this regard, we utilized a tumor-targeting cell-penetration peptide, p28, as a therapeutic agent to improve the efficacy of a current chemotherapeutic agent for GBM, and as a carrier for a fluorescence imaging agent for a clear identification of GBM. Here, we show that a near-infrared (NIR) imaging agent, ICG-p28 (a chemical conjugate of an FDA-approved NIR dye, indocyanine green ICG, and tumor-targeting p28 peptide) can preferentially localize tumors in multiple GBM animal models. Moreover, xenograft studies show that p28, as a therapeutic agent, can enhance the cytotoxic activity of temozolomide (TMZ), one of the few effective drugs for brain tumors. Collectively, our findings highlight the important role of the tumor-targeting peptide, which has great potential for intraoperative image-guided surgery and the development of new therapeutic strategies for GBM.

The Pathogenic Sphingolipid Psychosine is Secreted in Extracellular Vesicles in the Brain of a Mouse Model of Krabbe Disease

Psychosine exerts most of its toxic effects by altering membrane dynamics with increased shedding of extracellular vesicles (EVs). In this study, we discovered that a fraction of psychosine produced in the brain of the Twitcher mouse, a model for Krabbe disease, is associated with secreted EVs. We evaluated the effects of attenuating EV secretion in the Twitcher brain by depleting ceramide production with an inhibitor of neutral sphingomyelinase 2, GW4869. Twitcher mice treated with GW4869 had decreased overall EV levels, reduced EV-associated psychosine and unexpectedly, correlated with increased disease severity. Notably, characterization of well-established, neuroanatomic hallmarks of disease pathology, such as demyelination and inflammatory gliosis, remained essentially unaltered in the brains of GW4869-treated Twitcher mice compared to vehicle-treated Twitcher controls. Further analysis of Twitcher brain pathophysiology is required to understand the mechanism behind early-onset disease severity in GW4869-treated mice. The results herein demonstrate that some pathogenic lipids like psychosine may be secreted using EV pathways. Our results highlight the relevance of this secretory mechanism as a possible contributor to spreading pathogenic lipids in neurological lipidoses.

CRISPR-Cas9 Knock-In of T513M and G41S Mutations in the Murine β-Galactosyl-Ceramidase Gene Re-capitulates Early-Onset and Adult-Onset Forms of Krabbe Disease

Krabbe Disease (KD) is a lysosomal storage disorder characterized by the genetic deficiency of the lysosomal enzyme β-galactosyl-ceramidase (GALC). Deficit or a reduction in the activity of the GALC enzyme has been correlated with the progressive accumulation of the sphingolipid metabolite psychosine, which leads to local disruption in lipid raft architecture, diffuse demyelination, astrogliosis, and globoid cell formation. The twitcher mouse, the most used animal model, has a nonsense mutation, which limits the study of how different mutations impact the processing and activity of GALC enzyme. To partially address this, we generated two new transgenic mouse models carrying point mutations frequently found in infantile and adult forms of KD. Using CRISPR-Cas9 gene editing, point mutations T513M (infantile) and G41S (adult) were introduced in the murine GALC gene and stable founders were generated. We show that GALC ^T513M/T513M mice are short lived, have the greatest decrease in GALC activity, have sharp increases of psychosine, and rapidly progress into a severe and lethal neurological phenotype. In contrast, GALC ^G41S/G41S mice have normal lifespan, modest decreases of GALC, and minimal psychosine accumulation, but develop adult mild inflammatory demyelination and slight declines in coordination, motor skills, and memory. These two novel transgenic lines offer the possibility to study the mechanisms by which two distinct GALC mutations affect the trafficking of mutated GALC and modify phenotypic manifestations in early- vs adult-onset KD.

Waning efficacy in a long-term AAV-mediated gene therapy study in the murine model of Krabbe disease

Neonatal AAV9-gene therapy of the lysosomal enzyme galactosylceramidase (GALC) significantly ameliorates central and peripheral neuropathology, prolongs survival, and largely normalizes motor deficits in Twitcher mice. Despite these therapeutic milestones, new observations identified the presence of multiple small focal demyelinating areas in the brain after 6-8 months. These lesions are in stark contrast to the diffuse, global demyelination that affects the brain of naive Twitcher mice. Late-onset lesions exhibited lysosomal alterations with reduced expression of GALC and increased psychosine levels. Furthermore, we found that lesions were closely associated with the extravasation of plasma fibrinogen and activation of the fibrinogen-BMP-SMAD-GFAP gliotic response. Extravasation of fibrinogen correlated with tight junction disruptions of the vasculature within the lesioned areas. The lesions were surrounded by normal appearing white matter. Our study shows that the dysregulation of therapeutic GALC was likely driven by the exhaustion of therapeutic AAV episomal DNA within the lesions, paralleling the presence of proliferating oligodendrocyte progenitors and glia. We believe that this is the first demonstration of diminishing expression in vivo from an AAV gene therapy vector with detrimental effects in the brain of a lysosomal storage disease animal model. The development of this phenotype linking localized loss of GALC activity with relapsing neuropathology in the adult brain of neonatally AAV-gene therapy-treated Twitcher mice identifies and alerts to possible late-onset reductions of AAV efficacy, with implications to other genetic leukodystrophies.

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.

Synaptic Function and Dysfunction in Lysosomal Storage Diseases

Lysosomal storage diseases (LSDs) with neurological involvement are inherited genetic diseases of the metabolism characterized by lysosomal dysfunction and the accumulation of undegraded substrates altering glial and neuronal function. Often, patients with neurological manifestations present with damage to the gray and white matter and irreversible neuronal decline. The use of animal models of LSDs has greatly facilitated studying and identifying potential mechanisms of neuronal dysfunction, including alterations in availability and function of synaptic proteins, modifications of membrane structure, deficits in docking, exocytosis, recycling of synaptic vesicles, and inflammation-mediated remodeling of synapses. Although some extrapolations from findings in adult-onset conditions such as Alzheimer's disease or Parkinson's disease have been reported, the pathogenetic mechanisms underpinning cognitive deficits in LSDs are still largely unclear. Without being fully inclusive, the goal of this mini-review is to present a discussion on possible mechanisms leading to synaptic dysfunction in LSDs.

Krabbe disease successfully treated via monotherapy of intrathecal gene therapy

Globoid cell leukodystrophy (GLD; Krabbe disease) is a progressive, incurable neurodegenerative disease caused by deficient activity of the hydrolytic enzyme galactosylceramidase (GALC). The ensuing cytotoxic accumulation of psychosine results in diffuse central and peripheral nervous system (CNS, PNS) demyelination. Presymptomatic hematopoietic stem cell transplantation (HSCT) is the only treatment for infantile-onset GLD; however, clinical outcomes of HSCT recipients often remain poor, and procedure-related morbidity is high. There are no effective therapies for symptomatic patients. Herein, we demonstrate in the naturally occurring canine model of GLD that presymptomatic monotherapy with intrathecal AAV9 encoding canine GALC administered into the cisterna magna increased GALC enzyme activity, normalized psychosine concentration, improved myelination, and attenuated inflammation in both the CNS and PNS. Moreover, AAV-mediated therapy successfully prevented clinical neurological dysfunction, allowing treated dogs to live beyond 2.5 years of age, more than 7 times longer than untreated dogs. Furthermore, we found that a 5-fold lower dose resulted in an attenuated form of disease, indicating that sufficient dosing is critical. Finally, postsymptomatic therapy with high-dose AAV9 also significantly extended lifespan, signifying a treatment option for patients for whom HSCT is not applicable. If translatable to patients, these findings would improve the outcomes of patients treated either pre- or postsymptomatically.

AAV-Mediated GALC Gene Therapy Rescues Alpha-Synucleinopathy in the Spinal Cord of a Leukodystrophic Lysosomal Storage Disease Mouse Model

Krabbe's disease (KD) is primarily a demyelinating disorder, but recent studies have identified the presence of neuronal protein aggregates in the brain, at least partially composed by alpha-synuclein (α-syn). The role of this protein aggregation in the pathogenesis of KD is largely unknown, but it has added KD to a growing list of lysosomal storage diseases that can be also be considered as proteinopathies. While the presence of these protein aggregates within the KD brain is now appreciated, the remainder of the central nervous system (CNS) remains uncharacterized. This study is the first to report the presence of thioflavin-S reactive inclusions throughout the spinal cord of both murine and human spinal tissue. Stereological analysis revealed the temporal and spatial accumulation of these inclusions within the neurons of the ventral spinal cord vs. those located in the dorsal cord. This study also confirmed that these thio-S positive accumulations are present within neuronal populations and are made up at least in part by α-syn in both the twitcher mouse and cord autopsied material from affected human patients. Significantly, neonatal gene therapy for galactosylceramidase, a treatment that strongly improves the survival and health of KD mice, but not bone marrow transplantation prevents the formation of these inclusions in spinal neurons. These results expand the understanding of α-syn protein aggregation within the CNS of individuals afflicted with KD and underlines the tractability of this problem via early gene therapy, with potential impact to other synucleinopathies such as PD.

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.

Deregulation of signalling in genetic conditions affecting the lysosomal metabolism of cholesterol and galactosyl-sphingolipids

The role of lipids in neuroglial function is gaining momentum in part due to a better understanding of how many lipid species contribute to key cellular signalling pathways at the membrane level. The description of lipid rafts as membrane domains composed by defined classes of lipids such as cholesterol and sphingolipids has greatly helped in our understanding of how cellular signalling can be regulated and compartmentalized in neurons and glial cells. Genetic conditions affecting the metabolism of these lipids greatly impact on how some of these signalling pathways work, providing a context to understand the biological function of the lipid. Expectedly, abnormal metabolism of several lipids such as cholesterol and galactosyl-sphingolipids observed in several metabolic conditions involving lysosomal dysfunction are often accompanied by neuronal and myelin dysfunction. This review will discuss the role of lysosomal biology in the context of deficiencies in the metabolism of cholesterol and galactosyl-sphingolipids and their impact on neural function in three genetic disorders: Niemann-Pick type C, Metachromatic leukodystrophy and Krabbe’s disease.

Macrophages Expressing GALC Improve Peripheral Krabbe Disease by a Mechanism Independent of Cross-Correction

Many therapies for lysosomal storage disorders rely on cross-correction of lysosomal enzymes. In globoid cell leukodystrophy (GLD), mutations in GALC cause psychosine accumulation, inducing demyelination, a neuroinflammatory "globoid" reaction and neurodegeneration. The efficiency of GALC cross-correction in vivo, the role of the GALC substrate galactosylceramide, and the origin of psychosine are poorly understood. Using a novel GLD model, we show that cross-correction does not occur efficiently in vivo and that Galc-deficient Schwann cells autonomously produce psychosine. Furthermore, macrophages require GALC to degrade myelin, as Galc-deficient macrophages are transformed into globoid cells by exposure to galactosylceramide and produce a more severe GLD phenotype. Finally, hematopoietic stem cell transplantation in patients reduces globoid cells in nerves, suggesting that the phagocytic response of healthy macrophages, rather than cross-correction, contributes to the therapeutic effect. Thus, GLD may be caused by at least two mechanisms: psychosine-induced demyelination and secondary neuroinflammation from galactosylceramide storage in macrophages.

Mass spectrometry imaging and LC/MS reveal decreased cerebellar phosphoinositides in Niemann-Pick type C1-null mice

Niemann-Pick disease type C1 (NPC1) is a lipid storage disorder in which cholesterol and glycosphingolipids accumulate in late endosomal/lysosomal compartments because of mutations in the NPC1 gene. A hallmark of NPC1 is progressive neurodegeneration of the cerebellum as well as visceral organ damage; however, the mechanisms driving this disease pathology are not fully understood. Phosphoinositides are phospholipids that play distinct roles in signal transduction and vesicle trafficking. Here, we utilized a consensus spectra analysis of MS imaging data sets and orthogonal LC/MS analyses to evaluate the spatial distribution of phosphoinositides and quantify them in cerebellar tissue from Npc1-null mice. Our results suggest significant depletion of multiple phosphoinositide species, including PI, PIP, and PIP₂, in the cerebellum of the Npc1-null mice in both whole-tissue lysates and myelin-enriched fractions. Additionally, we observed altered levels of the regulatory enzyme phosphatidylinositol 4-kinase type 2α in Npc1-null mice. In contrast, the levels of related kinases, phosphatases, and transfer proteins were unaltered in the Npc1-null mouse model, as observed by Western blot analysis. Our discovery of phosphoinositide lipid biomarkers for NPC1 opens new perspectives on the pathophysiology underlying this fatal neurodegenerative disease.

Lead Optimization of Benzoxazolone Carboxamides as Orally Bioavailable and CNS Penetrant Acid Ceramidase Inhibitors

Sphingolipids (SphLs) are a diverse class of molecules that are regulated by a complex network of enzymatic pathways. A disturbance in these pathways leads to lipid accumulation and initiation of several SphL-related disorders. Acid ceramidase is one of the key enzymes that regulate the metabolism of ceramides and glycosphingolipids, which are important members of the SphL family. Herein, we describe the lead optimization studies of benzoxazolone carboxamides resulting in piperidine 22m, where we demonstrated target engagement in two animal models of neuropathic lysosomal storage diseases (LSDs), Gaucher’s and Krabbe’s diseases. After daily intraperitoneal administration at 90 mg kg^–1, 22m significantly reduced the brain levels of the toxic lipids glucosylsphingosine (GluSph) in 4L;C* mice and galactosylsphingosine (GalSph) in Twitcher mice. We believe that 22m is a lead molecule that can be further developed for the correction of severe neurological LSDs where GluSph or GalSph play a significant role in disease pathogenesis.

Inhibition of the IGF-1-PI3K-Akt-mTORC2 pathway in lipid rafts increases neuronal vulnerability in a genetic lysosomal glycosphingolipidosis

Glycosphingolipid (GSL) accumulation is implicated in the neuropathology of several lysosomal conditions, such as Krabbe disease, and may also contribute to neuronal and glial dysfunction in adult-onset conditions such as Parkinson's disease, Alzheimer's disease and multiple sclerosis. GSLs accumulate in cellular membranes and disrupt their structure; however, how membrane disruption leads to cellular dysfunction remains unknown. Using authentic cellular and animal models for Krabbe disease, we provide a mechanism explaining the inactivation of lipid raft (LR)-associated IGF-1-PI3K-Akt-mTORC2, a pathway of crucial importance for neuronal function and survival. We show that psychosine, the GSL that accumulates in Krabbe disease, leads to a dose-dependent LR-mediated inhibition of this pathway by uncoupling IGF-1 receptor phosphorylation from downstream Akt activation. This occurs by interfering with the recruitment of PI3K and mTORC2 to LRs. Akt inhibition can be reversed by sustained IGF-1 stimulation, but only during a time window before psychosine accumulation reaches a threshold level. Our study shows a previously unknown connection between LR-dependent regulation of mTORC2 activity at the cell surface and a genetic neurodegenerative disease. Our results show that LR disruption by psychosine desensitizes cells to extracellular growth factors by inhibiting signal transmission from the plasma membrane to intracellular compartments. This mechanism serves also as a mechanistic model to understand how alterations of the membrane architecture by the progressive accumulation of lipids undermines cell function, with potential implications in other genetic sphingolipidoses and adult neurodegenerative conditions. This article has an associated First Person interview with the first author of the paper.

Psychosine remodels model lipid membranes at neutral pH

β-Galactosylsphingosine or psychosine (PSY) is a single chain sphingolipid with a cationic group, which is degraded in the lysosome lumen by β-galactosylceramidase during sphingolipid biosynthesis. A deficiency of this enzyme activity results in Krabbe's disease and PSY accumulation. This favors its escape to extralysosomal spaces, with its pH changing from acidic to neutral. We studied the interaction of PSY with model lipid membranes in neutral conditions, using phospholipid vesicles and monolayers as classical model systems, as well as a complex lipid mixture that mimics the lipid composition of myelin. At pH 7.4, when PSY is mainly neutral, it showed high surface activity, self-organizing into large structures, probably lamellar in nature, with a CMC of 38 ± 3 μM. When integrated into phospholipid membranes, PSY showed preferential partition into disordered phases, shifting phase equilibrium. The presence of PSY reduces the compactness of the membrane, making it more easily compressible. It also induces lipid domain disruption in vesicles composed of the main myelin lipids. The surface electrostatics of lipid membranes was altered by PSY in a complex manner. A shift to positive zeta potential values evidenced its presence in the vesicles. Furthermore, the increase of surface potential and surface water structuring observed may be a consequence of its location at the interface of the positively charged layer. As Krabbe's disease is a demyelinating process, PSY alteration of the membrane phase state, lateral lipid distribution and surface electrostatics appears important to the understanding of myelin destabilization at the supramolecular level.

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.

Long-Term Improvement of Neurological Signs and Metabolic Dysfunction in a Mouse Model of Krabbe's Disease after Global Gene Therapy

We report a global adeno-associated virus (AAV)9-based gene therapy protocol to deliver therapeutic galactosylceramidase (GALC), a lysosomal enzyme that is deficient in Krabbe's disease. When globally administered via intrathecal, intracranial, and intravenous injections to newborn mice affected with GALC deficiency (twitcher mice), this approach largely surpassed prior published benchmarks of survival and metabolic correction, showing long-term protection of demyelination, neuroinflammation, and motor function. Bone marrow transplantation, performed in this protocol without immunosuppressive preconditioning, added minimal benefits to the AAV9 gene therapy. Contrasting with other proposed pre-clinical therapies, these results demonstrate that achieving nearly complete correction of GALC's metabolic deficiencies across the entire nervous system via gene therapy can have a significant improvement to behavioral deficits, pathophysiological changes, and survival. These results are an important consideration for determining the safest and most effective manner for adapting gene therapy to treat this leukodystrophy in the clinic.

Analysis of age-related changes in psychosine metabolism in the human brain

α-Synuclein aggregation has been linked to Gaucher’s disease (GD) and Krabbe’s disease (KD), lysosomal conditions affecting glycosphingolipid metabolism. α-Synuclein pathology has been directly attributed to the dysregulation of glycosphingolipids in both conditions, specifically to increased galactosylsphingosine (psychosine) content in the context of KD. Furthermore, the gene (GALC) coding for the psychosine degrading enzyme galactosylceramidase (GALC), has recently been identified as a risk loci for Parkinson’s disease. However, it is unknown if changes in psychosine metabolism and GALC activity in the context of the aging human brain correlate with Parkinson’s disease. We investigated psychosine accumulation and GALC activity in the aging brain using fresh frozen post-mortem tissue from Parkinson’s (PD, n = 10), Alzheimer’s (AD, n = 10), and healthy control patients (n = 9), along with tissue from neuropsychiatric patients (schizophrenia, bipolar disorder and depression, n = 15 each). An expanded mutational analysis of PD (n = 20), AD (n = 10), and healthy controls (n = 30) examined if PD was correlated with carriers for severe GALC mutations. Psychosine content within the cerebral cortex of PD patients was elevated above control patients. Within all patients, psychosine displayed a significant (p<0.05) and robust regional distribution in the brain with higher levels in the white matter and substantia nigra. A mutational analysis revealed an increase in the incidence of severe GALC mutations within the PD patient population compared to the cohorts of Alzheimer’s patients and healthy controls tested. In addition to α-synuclein pathology identified in the KD brain, control patients identified as GALC mutational carriers or possessing a GALC pathogenic variant had evidence of α-synuclein pathology, indicating a possible correlation between α-synuclein pathology and dysregulation of psychosine metabolism in the adult brain. Carrier status for GALC mutations and prolonged exposure to increased psychosine could contribute to α-synuclein pathology, supporting psychosine metabolism by galactosylceramidase as a risk factor for Parkinson’s disease.

microRNA-219 Reduces Viral Load and Pathologic Changes in Theiler's Virus-Induced Demyelinating Disease

Analysis of microRNA (miR) expression in the central nervous system white matter of SJL mice infected with the BeAn strain of Theiler's murine encephalomyelitis virus (TMEV) revealed a significant reduction of miR-219, a critical regulator of myelin assembly and repair. Restoration of miR-219 expression by intranasal administration of a synthetic miR-219 mimic before disease onset ameliorates clinical disease, reduces neurogliosis, and partially recovers motor and sensorimotor function by negatively regulating proinflammatory cytokines and virus RNA replication. Moreover, RNA sequencing of host lesions showed that miR-219 significantly downregulated two genes essential for the biosynthetic cholesterol pathway, Cyp51 (lanosterol 14-α-demethylase) and Srebf1 (sterol regulatory element-binding protein-1), and reduced cholesterol biosynthesis in infected mice and rat CG-4 glial precursor cells in culture. The change in cholesterol biosynthesis had both anti-inflammatory and anti-viral effects. Because RNA viruses hijack endoplasmic reticulum double-layered membranes to provide a platform for RNA virus replication and are dependent on endogenous pools of cholesterol, miR-219 interference with cholesterol biosynthesis interfered virus RNA replication. These findings demonstrate that miR-219 inhibits TMEV-induced demyelinating disease through its anti-inflammatory and anti-viral properties.

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.

A microglial hypothesis of globoid cell leukodystrophy pathology

Globoid cell leukodystrophy (GLD), also known as Krabbe's disease, is a fatal demyelinating disease accompanied by the formation of giant, multinucleated cells called globoid cells. Previously believed to be a byproduct of inflammation, these cells can be found early in disease before evidence of any damage. The precise mechanism by which these globoid cells cause oligodendrocyte dysfunction is not completely understood, nor is their cell type defined. This Review outlines the idea that microglial cells are transformed into an unknown and undefined novel M3 phenotype in GLD, which is cytotoxic to oligodendrocytes, leading to disease progression. © 2016 Wiley Periodicals, Inc.

Port-to-port delivery: Mobilization of toxic sphingolipids via extracellular vesicles

The discovery that most cells produce extracellular vesicles (EVs) and release them in the extracellular milieu has spurred the idea that these membranous cargoes spread pathogenic mechanisms. In the brain, EVs may have multifold and important physiological functions, from deregulating synaptic activity to promoting demyelination to changes in microglial activity. The finding that small EVs (exosomes) contain α-synuclein and β-amyloid, among other pathogenic proteins, is an example of this notion, underscoring their potential role in the brains of patients with Parkinson's and Alzheimer's diseases. Given that they are membranous vesicles, we speculate that EVs also have an intrinsic capacity to incorporate sphingolipids. In conditions under which these lipids are elevated to toxic levels, such as in Krabbe's disease and metachromatic leukodystrophy, EVs may contribute to spread disease from sick to healthy cells. In this essay, we discuss a working hypothesis that brain cells in sphingolipidoses clear some of the accumulated lipid material to attempt restoring cell homeostasis via EV secretion. We hypothesize that secreted sphingolipid-loaded EVs shuttle pathogenic lipids to cells that are not intrinsically affected, contributing to establishing non-cell-autonomous defects. © 2016 Wiley Periodicals, Inc.

Fluid levity of the cell: Role of membrane lipid architecture in genetic sphingolipidoses

Sphingolipidoses arise from inherited loss of function of key enzymes regulating the sphingolipid (SL) metabolism and the accumulation of large quantities of these lipids in affected cells. Most frequently, toxicity is manifested in the nervous system, where survival and function of neurons and glial cells are most affected. Although detailed information is available on neuroglial alterations during terminal stages of the disease, the initial pathogenic mechanisms triggering neuropathology are largely unclear. Because they are key components of biological membranes, changes in the local concentration of SLs are likely to impact the organization of membrane domains and functions. This Commentary proposes that SL toxicity involves initial defects in the integrity of lipid domains, membrane fluidity, and membrane bending, leading to membrane deformation and deregulation of cell signaling and function. Understanding how SLs alter membrane architecture may provide breakthroughs for more efficient treatment of sphingolipidoses. © 2016 Wiley Periodicals, Inc.

Hematopoietic Stem cell transplantation and lentiviral vector-based gene therapy for Krabbe's disease: Present convictions and future prospects

Currently, presymtomatic hematopoietic stem and progenitor cell transplantation (HSPCT) is the only therapeutic modality that alleviates Krabbe's disease (KD)‐induced central nervous system damage. However, all HSPCT‐treated patients exhibit severe deterioration in peripheral nervous system function characterized by major motor and expressive language pathologies. We hypothesize that a combination of several mechanisms contribute to this phenomenon, including 1) nonoptimal conditioning protocols with consequent inefficient engraftment and biodistribution of donor‐derived cells and 2) insufficient uptake of donor cell‐secreted galactocerebrosidease (GALC) secondary to a naturally low expression level of the cation‐independent mannose 6‐phosphate‐receptor (CI‐MPR). We have characterized the effects of a busulfan (Bu) based conditioning regimen on the efficacy of HSPCT in prolonging twi mouse average life span. There was no correlation between the efficiency of bone marrow engraftment of donor cells and twi mouse average life span. HSPCT prolonged the average life span of twi mice, which directly correlated with the aggressiveness of the Bu‐mediated conditioning protocols. HSPC transduced with lentiviral vectors carrying the GALC cDNA under control of cell‐specific promoters were efficiently engrafted in twi mouse bone marrow. To facilitate HSPCT‐mediated correction of GALC deficiency in target cells expressing low levels of CI‐MPR, a novel GALC fusion protein including the ApoE1 receptor was developed. Efficient cellular uptake of the novel fusion protein was mediated by a mannose‐6‐phosphate‐independent mechanism. The novel findings described here elucidate some of the cellular mechanisms that impede the cure of KD patients by HSPCT and concomitantly open new directions to enhance the therapeutic efficacy of HSPCT protocols for KD. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

How membrane dysfunction influences neuronal survival pathways in sphingolipid storage disorders

Sphingolipidoses are a class of inherited diseases that result from the toxic accumulation of undigested sphingolipids in lysosomes and other cellular membranes. Sphingolipids are particularly enriched in cells of the nervous system, and their excessive accumulation during disease has a significant impact on the nervous system. Neuronal dysfunction followed by neurological compromise is a common feature in many of these diseases; however, the underlying mechanisms that cause vulnerability of neurons are not fully understood. The plasma membrane plays a critical role in regulating cellular survival pathways, and its dysfunction has been implicated in neuronal failure in various adult-onset neuropathies. In the context of sphingolipidoses, we hypothesize that gradual accumulation of undigested lipids in plasma membranes causes local disruptions in lipid raft domains, leading to deregulation of multiple signaling pathways important for neuronal survival and function. We propose that defects in downstream signaling as a result of membrane dysfunction are common mechanisms underlying neuronal vulnerability in sphingolipid storage disorders with neurological compromise. © 2016 Wiley Periodicals, Inc.

Synaptic failure: The achilles tendon of sphingolipidoses

The presence of life-threatening neurological symptoms in more than two-thirds of lysosomal storage diseases (LSDs) underscores how vulnerable the nervous system is to lysosomal failure. Neurological dysfunction in LSDs has historically been attributed to the disruption of neuronal and glial homeostasis resulting from the progressive jamming of the endosomal/lysosomal pathway. In neurons, a dysfunctional endosomal-lysosomal system can elicit dire consequences. Given that neurons are largely postmitotic after birth, one can clearly understand that the inability of these cells to proliferate obliterates any possibility of diluting stored lysosomal material by means of cellular division. At its most advanced stage, this situation constitutes a terminal factor in neuronal life, resulting in cell death. However, synaptic deficits in the absence of classical neuronal cell death appear to be common features during the early stages in many LSDs, particularly sphingolipidoses. In essence, failure of synapses to convey their messages, even without major structural damage to the neuronal bodies, is a form of physiological death. This concept of dying-back neuropathology is highly relevant not only for understanding the dynamics of the neurological decline in these diseases, but, more importantly; it might also constitute an important target for molecular therapies to protect perhaps the "Achilles" point in the entire physiological architecture of the brain, thus avoiding an irreversible journey to neuronal demise. © 2016 Wiley Periodicals, Inc.

SVCT2 Expression and Function in Reactive Astrocytes Is a Common Event in Different Brain Pathologies

Ascorbic acid (AA), the reduced form of vitamin C, acts as a neuroprotector by eliminating free radicals in the brain. Sodium/vitamin C co-transporter isoform 2 (SVCT2) mediates uptake of AA by neurons. It has been reported that SVCT2 mRNA is induced in astrocytes under ischemic damage, suggesting that its expression is enhanced in pathological conditions. However, it remains to be established if SVCT expression is altered in the presence of reactive astrogliosis generated by different brain pathologies. In the present work, we demonstrate that SVCT2 expression is increased in astrocytes present at sites of neuroinflammation induced by intracerebroventricular injection of a GFP-adenovirus or the microbial enzyme, neuraminidase. A similar result was observed at 5 and 10 days after damage in a model of traumatic injury and in the hippocampus and cerebral cortex in the in vivo kindling model of epilepsy. Furthermore, we defined that cortical astrocytes maintained in culture for long periods acquire markers of reactive gliosis and express SVCT2, in a similar way as previously observed in situ. Finally, by means of second harmonic generation and 2-photon fluorescence imaging, we analyzed brain necropsied material from patients with Alzheimer's disease (AD), which presented with an accumulation of amyloid plaques. Strikingly, although AD is characterized by focalized astrogliosis surrounding amyloid plaques, SVCT2 expression at the astroglial level was not detected. We conclude that SVCT2 is heterogeneously induced in reactive astrogliosis generated in different pathologies affecting the central nervous system (CNS).

miR-219 Cooperates with miR-338 in Myelination and Promotes Myelin Repair in the CNS

A lack of sufficient oligodendrocyte myelination contributes to remyelination failure in demyelinating disorders. miRNAs have been implicated in oligodendrogenesis; however, their functions in myelin regeneration remained elusive. Through developmentally regulated targeted mutagenesis, we demonstrate that miR-219 alleles are critical for CNS myelination and remyelination after injury. Further deletion of miR-338 exacerbates the miR-219 mutant hypomyelination phenotype. Conversely, miR-219 overexpression promotes precocious oligodendrocyte maturation and regeneration processes in transgenic mice. Integrated transcriptome profiling and biotin-affinity miRNA pull-down approaches reveal stage-specific miR-219 targets in oligodendrocytes and further uncover a novel network for miR-219 targeting of differentiation inhibitors including Lingo1 and Etv5. Inhibition of Lingo1 and Etv5 partially rescues differentiation defects of miR-219-deficient oligodendrocyte precursors. Furthermore, miR-219 mimics enhance myelin restoration following lysolecithin-induced demyelination as well as experimental autoimmune encephalomyelitis, principal animal models of multiple sclerosis. Together, our findings identify context-specific miRNA-regulated checkpoints that control myelinogenesis and a therapeutic role for miR-219 in CNS myelin repair.

Psychosine enhances the shedding of membrane microvesicles: Implications in demyelination in Krabbe's disease

In prior studies, our laboratory showed that psychosine accumulates and disrupts lipid rafts in brain membranes of Krabbe’s disease. A model of lipid raft disruption helped explaining psychosine’s effects on several signaling pathways important for oligodendrocyte survival and differentiation but provided more limited insight in how this sphingolipid caused demyelination. Here, we have studied how this cationic inverted coned lipid affects the fluidity, stability and structure of myelin and plasma membranes. Using a combination of cutting-edge imaging techniques in non-myelinating (red blood cell), and myelinating (oligodendrocyte) cell models, we show that psychosine is sufficient to disrupt sphingomyelin-enriched domains, increases the rigidity of localized areas in the plasma membrane, and promotes the shedding of membranous microvesicles. The same physicochemical and structural changes were measured in myelin membranes purified from the mutant mouse Twitcher, a model for Krabbe’s disease. Areas of higher rigidity were measured in Twitcher myelin and correlated with higher levels of psychosine and of myelin microvesiculation. These results expand our previous analyses and support, for the first time a pathogenic mechanism where psychosine’s toxicity in Krabbe disease involves deregulation of cell signaling not only by disruption of membrane rafts, but also by direct local destabilization and fragmentation of the membrane through microvesiculation. This model of membrane disruption may be fundamental to introduce focal weak points in the myelin sheath, and consequent diffuse demyelination in this leukodystrophy, with possible commonality to other demyelinating disorders.

Generation of a LacZ reporter transgenic mouse line for the stereological analysis of oligodendrocyte loss in galactosylceramidase deficiency

Krabbe's disease is a leukodystrophy resulting from deficiency of galactosylceramidase and the accumulation of galactosylsphingosine (psychosine) in the nervous system. Psychosine is believed to cause central demyelination by killing oligodendrocytes. Quantitative analysis of this process is lacking. To address this, we generated a new transgenic reporter twitcher line in which myelinating oligodendrocytes are genetically marked by the expression of LacZ under control of the myelin basic protein (MBP) promoter. MBP-LacZ-twitcher transgenic mice were used for unbiased stereological quantification of β-galactosidase+ oligodendrocytes in the spinal cord. As expected, we found decreased numbers of these cells in mutant cords, paralleling the severity of clinical disease. The decrease of oligodendrocytes does not correlate well with the increase of psychosine. The new MBP-LacZ-twitcher line will be a useful genetic tool for measuring changes in oligodendrocyte numbers in different regions of the mutant CNS and in preclinical trials of therapies to prevent demyelination. © 2016 Wiley Periodicals, Inc.

Beyond Krabbe's disease: The potential contribution of galactosylceramidase deficiency to neuronal vulnerability in late-onset synucleinopathies

New insights into the pathophysiological mechanisms behind late-onset neurodegenerative diseases have come from unexpected sources in recent years. Specifically, the group of inherited metabolic disorders known as lysosomal storage diseases that most commonly affect infants has been found to have surprising similarities with adult neurodegenerative disorders. Most notable has been the identification of Gaucher's disease as a comorbidity for Parkinson's disease. Prompted by the recent identification of neuronal aggregates of α-synuclein in another lysosomal storage disease, Krabbe's disease, we propose the idea that a similar connection exists between adult synucleinopathies and Krabbe's. Similarities between the two diseases, including the pattern of α-synuclein aggregation in the brain of the twitcher mouse (the authentic murine model of Krabbe's disease), changes to lipid membrane dynamics, and possible dysfunction in synaptic function and macroautophagy, underscore a link between Krabbe's disease and late-onset synucleinopathies. Silent GALC mutations may even constitute a risk factor for the development of Parkinson's in certain patients. More research is required to identify definitively any link and the validity of this hypothesis, but such a connection would prove invaluable for developing novel therapeutic targets for Parkinson's based on our current understanding of Krabbe's disease and for establishing new biomarkers for the identification of at-risk patients. © 2016 Wiley Periodicals, Inc.

Recent progress on lipid lateral heterogeneity in plasma membranes: From rafts to submicrometric domains

The concept of transient nanometric domains known as lipid rafts has brought interest to reassess the validity of the Singer-Nicolson model of a fluid bilayer for cell membranes. However, this new view is still insufficient to explain the cellular control of surface lipid diversity or membrane deformability. During the past decades, the hypothesis that some lipids form large (submicrometric/mesoscale vs nanometric rafts) and stable (>min vs s) membrane domains has emerged, largely based on indirect methods. Morphological evidence for stable submicrometric lipid domains, well-accepted for artificial and highly specialized biological membranes, was further reported for a variety of living cells from prokaryot es to yeast and mammalian cells. However, results remained questioned based on limitations of available fluorescent tools, use of poor lipid fixatives, and imaging artifacts due to non-resolved membrane projections. In this review, we will discuss recent evidence generated using powerful and innovative approaches such as lipid-specific toxin fragments that support the existence of submicrometric domains. We will integrate documented mechanisms involved in the formation and maintenance of these domains, and provide a perspective on their relevance on membrane deformability and regulation of membrane protein distribution.

Mechanism of neuromuscular dysfunction in Krabbe disease

The atrophy of skeletal muscles in patients with Krabbe disease is a major debilitating manifestation that worsens their quality of life and limits the clinical efficacy of current therapies. The pathogenic mechanism triggering muscle wasting is unknown. This study examined structural, functional, and metabolic changes conducive to muscle degeneration in Krabbe disease using the murine (twitcher mouse) and canine [globoid cell leukodystrophy (GLD) dog] models. Muscle degeneration, denervation, neuromuscular [neuromuscular junction (NMJ)] abnormalities, and axonal death were investigated using the reporter transgenic twitcher-Thy1.1-yellow fluorescent protein mouse. We found that mutant muscles had significant numbers of smaller-sized muscle fibers, without signs of regeneration. Muscle growth was slow and weak in twitcher mice, with decreased maximum force. The NMJ had significant levels of activated caspase-3 but limited denervation. Mutant NMJ showed reduced surface areas and lower volumes of presynaptic terminals, with depressed nerve control, increased miniature endplate potential (MEPP) amplitude, decreased MEPP frequency, and increased rise and decay rate constants. Twitcher and GLD dog muscles had significant capacity to store psychosine, the neurotoxin that accumulates in Krabbe disease. Mechanistically, muscle defects involved the inactivation of the Akt pathway and activation of the proteasome pathway. Our work indicates that muscular dysfunction in Krabbe disease is compounded by a pathogenic mechanism involving at least the failure of NMJ function, activation of proteosome degradation, and a reduction of the Akt pathway. Akt, which is key for muscle function, may constitute a novel target to complement in therapies for Krabbe disease.

An in vitro model for the study of cellular pathophysiology in globoid cell leukodystrophy

The precise function of multi-nucleated microglia, called globoid cells, that are uniquely abundant in the central nervous system of globoid cell leukodystrophy (GLD) is unclear. This gap in knowledge has been hindered by the lack of an appropriate in vitro model for study. Herein, we describe a primary murine glial culture system in which treatment with psychosine results in multinucleation of microglia resembling the characteristic globoid cells found in GLD. Using this novel system, we defined the conditions and modes of analysis for study of globoid cells. The potential use of this model system was validated in our previous study, which identified a potential role for matrix metalloproteinase (MMP)-3 in GLD. This novel in vitro system may be a useful model in which to study the formation and function, but also the potential therapeutic manipulation, of these unique cells.

Neuronal inclusions of α-synuclein contribute to the pathogenesis of Krabbe disease

Demyelination is a major contributor to the general decay of neural functions in children with Krabbe disease. However, recent reports have indicated a significant involvement of neurons and axons in the neuropathology of the disease. In this study, we have investigated the nature of cellular inclusions in the Krabbe brain. Brain samples from the twitcher mouse model for Krabbe disease and from patients affected with the infantile and late-onset forms of the disease were examined for the presence of neuronal inclusions. Our experiments demonstrated the presence of cytoplasmic aggregates of thioflavin-S-reactive material in both human and murine mutant brains. Most of these inclusions were associated with neurons. A few inclusions were detected to be associated with microglia and none were associated with astrocytes or oligodendrocytes. Thioflavin-S-reactive inclusions increased in abundance, paralleling the development of neurological symptoms, and distributed throughout the twitcher brain in areas of major involvement in cognition and motor functions. Electron microscopy confirmed the presence of aggregates of stereotypic β-sheet folded proteinaceous material. Immunochemical analyses identified the presence of aggregated forms of α-synuclein and ubiquitin, proteins involved in the formation of Lewy bodies in Parkinson's disease and other neurodegenerative conditions. In vitro assays demonstrated that psychosine, the neurotoxic sphingolipid accumulated in Krabbe disease, accelerated the fibrillization of α-synuclein. This study demonstrates the occurrence of neuronal deposits of fibrillized proteins including α-synuclein, identifying Krabbe disease as a new α-synucleinopathy.

Characterization and application of a disease-cell model for a neurodegenerative lysosomal disease

Disease-cell models that recapitulate specific molecular phenotypes are essential for the investigation of molecular pathogenesis of neurodegenerative diseases including lysosomal storage diseases (LSDs) with predominant neurological manifestations. Herein we report the development and characterization of a cell model for a rapid neurodegenerative LSDs, globoid-cell leukodystrophy (GLD), mostly known as Krabbe disease. GLD is caused by the deficiency of β-galactocerebrosidase (GALC), a lysosomal enzyme that hydrolyzes two glycosphingolipids, psychosine and galactosylceramide. Unfortunately, the available culture fibroblasts from GLD patients consist of a limited research tool as these cells fail to accumulate psychosine, the central pathogenic glycosphingolipid in this LSD that results in severe demyelination. Firstly, we obtained brain samples from the Twitcher (Twi) mice (GALC(twi/twi)), the natural mouse model with GALC deficiency. We immortalized the primary neuroglial cultured cells with SV40 large T antigen, generating the 145M-Twi and the 145C-Wt cell lines from the Twi and control mice, respectively. Both cell lines expressed specific oligodendrocyte markers including A2B5 and GalC. The 145M-Twi cells showed biochemical and cellular disturbances related to GLD neuropathogenesis including remarkable caspase-3 activation, release of cytochrome C into the cytosol and expansion of the lysosomal compartment. Under treatment with glycosphingolipids, 145M-Twi cells showed increased LC3B levels, a marker of autophagy. Using the LC-MS/MS method that we developed, the 145M-Twi cells showed significantly higher levels of psychosine. The 145M-Twi and 145C-Wt lines allowed the development of a robust throughput LC-MS/MS assay to measure cellular psychosine levels. In this throughput assay, l-cycloserine showed to significantly reduce the 145M-Twi cellular levels of psychosine. The established 145M-Twi cells are powerful research tools to investigate the neurologically relevant pathogenic pathways as well as to develop primary screening assays for the identification of therapeutic agents for GLD and potentially other glycosphingolipid disorders.

Unconventional Neurogenic Niches and Neurogenesis Modulation by Vitamins

Although the generation of new neurons occurs in adult mammals, it has been classically described in two defined regions of the brain denominated neurogenic niches: the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus. In these regions, neural stem cells give rise to new neurons and glia, which functionally integrate into the existing circuits under physiological conditions. However, accumulating evidence indicates the presence of neurogenic potential in other brain regions, from which multipotent precursors can be isolated and differentiated in vitro. In some of these regions, neuron generation occurs at low levels; however, the addition of growth factors, hormones or other signaling molecules increases the proliferation and differentiation of precursor cells. In addition, vitamins, which are micronutrients necessary for normal brain development, and whose deficiency produces neurological impairments, have a regulatory effect on neural stem cells in vitro and in vivo. In the present review, we will describe the progress that has been achieved in determining the neurogenic potential in other regions, known as unconventional niches, as well as the characteristics of the neural stem cells described for each region. Finally, we will revisit the roles of commonly known vitamins as modulators of precursor cell proliferation and differentiation, and their role in the complex and tight molecular signaling that impacts these neurogenic niches.

Vitamin C Transporters, Recycling and the Bystander Effect in the Nervous System: SVCT2 versus Gluts

Vitamin C is an essential micronutrient in the human diet; its deficiency leads to a number of symptoms and ultimately death. After entry into cells within the central nervous system (CNS) through sodium vitamin C transporters (SVCTs) and facilitative glucose transporters (GLUTs), vitamin C functions as a neuromodulator, enzymatic cofactor, and reactive oxygen species (ROS) scavenger; it also stimulates differentiation. In this review, we will compare the molecular and structural aspects of vitamin C and glucose transporters and their expression in endothelial or choroid plexus cells, which form part of the blood-brain barrier and blood-cerebrospinal fluid (CSF) barrier, respectively. Additionally, we will describe SVCT and GLUT expression in different cells of the brain as well as SVCT2 distribution in tanycytes and astrocytes of the hypothalamic region. Finally, we will describe vitamin C recycling in the brain, which is mediated by a metabolic interaction between astrocytes and neurons, and the role of the "bystander effect" in the recycling mechanism of vitamin C in both normal and pathological conditions.

Inhibition of angiogenesis by β-galactosylceramidase deficiency in globoid cell leukodystrophy

Globoid cell leukodystrophy (Krabbe disease) is a neurological disorder of infants caused by genetic deficiency of the lysosomal enzyme β-galactosylceramidase leading to accumulation of the neurotoxic metabolite 1-β-d-galactosylsphingosine (psychosine) in the central nervous system. Angiogenesis plays a pivotal role in the physiology and pathology of the brain. Here, we demonstrate that psychosine has anti-angiogenic properties by causing the disassembling of endothelial cell actin structures at micromolar concentrations as found in the brain of patients with globoid cell leukodystrophy. Accordingly, significant alterations of microvascular endothelium were observed in the post-natal brain of twitcher mice, an authentic model of globoid cell leukodystrophy. Also, twitcher endothelium showed a progressively reduced capacity to respond to pro-angiogenic factors, defect that was corrected after transduction with a lentiviral vector harbouring the murine β-galactosylceramidase complementary DNA. Finally, RNA interference-mediated β-galactosylceramidase gene silencing causes psychosine accumulation in human endothelial cells and hampers their mitogenic and motogenic response to vascular endothelial growth factor. Accordingly, significant alterations were observed in human microvasculature from brain biopsy of a globoid cell leukodystrophy case. Together these data demonstrate that β-galactosylceramidase deficiency induces significant alterations in endothelial neovascular responses that may contribute to central nervous system and systemic damages that occur in globoid cell leukodystrophy.

The sphingolipid psychosine inhibits fast axonal transport in Krabbe disease by activation of GSK3β and deregulation of molecular motors

Loss of function of galactosylceramidase lysosomal activity causes demyelination and vulnerability of various neuronal populations in Krabbe disease. Psychosine, a lipid-raft-associated sphingolipid that accumulates in this disease, is thought to trigger these abnormalities. Myelin-free in vitro analyses showed that psychosine inhibited fast axonal transport through the activation of axonal PP1 and GSK3β in the axon. Abnormal levels of activated GSK3β and abnormally phosphorylated kinesin light chains were found in nerve samples from a mouse model of Krabbe disease. Administration of GSK3β inhibitors significantly ameliorated transport defects in vitro and in vivo in peripheral axons of the mutant mouse. This study identifies psychosine as a pathogenic sphingolipid able to block fast axonal transport and is the first to provide a molecular mechanism underlying dying-back degeneration in this genetic leukodystrophy.

Missense mutation in mouse GALC mimics human gene defect and offers new insights into Krabbe disease

Krabbe disease is a devastating pediatric leukodystrophy caused by mutations in the galactocerebrosidase (GALC) gene. A significant subset of the infantile form of the disease is due to missense mutations that result in aberrant protein production. The currently used mouse model, twitcher, has a nonsense mutation not found in Krabbe patients, although it is similar to the human 30 kb deletion in abrogating GALC expression. Here, we identify a spontaneous mutation in GALC, GALCtwi-5J, that precisely matches the E130K missense mutation in patients with infantile Krabbe disease. GALCtwi-5J homozygotes show loss of enzymatic activity despite normal levels of precursor protein, and manifest a more severe phenotype than twitcher, with half the life span. Although neuropathological hallmarks such as gliosis, globoid cells and psychosine accumulation are present throughout the nervous system, the CNS does not manifest significant demyelination. In contrast, the PNS is severely hypomyelinated and lacks large diameter axons, suggesting primary dysmyelination, rather than a demyelinating process. Our data indicate that early demise is due to mechanisms other than myelin loss and support an important role for neuroinflammation in Krabbe disease progression. Furthermore, our results argue against a causative relationship between psychosine accumulation, white matter loss and gliosis.

MMP-3 mediates psychosine-induced globoid cell formation: implications for leukodystrophy pathology

Globoid cell leukodystrophy (GLD) or Krabbe disease, is a fatal demyelinating disease attributed to mutations in the galactocerebrosidase (GALC) gene. Loss of function mutations in GALC result in accumulation of the glycolipid intermediate, galactosylsphingosine (psychosine). Due to the cytotoxicity of psychosine, it has been hypothesized that accumulated psychosine underlie the pathophysiology of GLD. However, the cellular mechanisms of GLD pathophysiology remain unclear. Globoid cells, multinucleated microglia/macrophages in the central nervous system (CNS), are a defining characteristic of GLD. Here we report that exposure of primary glial cultures to psychosine induces the expression and the production of matrix metalloproteinase (MMP)-3 that mediated a morphological transformation of microglia into a multinucleated globoid cell type. Additionally, psychosine-induced globoid cell formation from microglia was prevented by either genetic ablation or chemical inhibition of MMP-3. These effects are microglia-specific as peripheral macrophages exposed to psychosine did not become activated or express increased levels of MMP-3. In the brain from twitcher mice, a murine model of human GLD, elevated MMP-3 expression relative to wild-type littermates was contemporaneous with disease onset and further increased with disease progression. Further, bone marrow transplantation (BMT), currently the only therapeutically beneficial treatment for GLD, did not mitigate the elevated expression of MMP-3 in twitcher mice. Hence, elevated expression of MMP-3 in GLD may promote microglial responses to psychosine that may represent an important pathophysiological process in this disease and its treatment.