Biochemistry and neuropathology of mice doubly deficient in synthesis and degradation of galactosylceramide

Promyelinating drugs ameliorate oligodendrocyte pathologies in a mouse model of Krabbe disease

Krabbe disease (KD) is a rare inherited demyelinating disorder caused by a deficiency in the lysosomal enzyme galactosylceramide (GalCer) β-galactosidase. Most patients with KD exhibit fatal cerebral demyelination with apoptotic oligodendrocyte (OL) death and die before the age of 2-4 years. We have previously reported that primary OLs isolated from the brains of twitcher (twi) mice, an authentic mouse model of KD, have cell-autonomous developmental defects and undergo apoptotic death accompanied by abnormal accumulation of psychosine, an endogenous cytotoxic lyso-derivative of GalCer. In this study, we aimed to investigate the effects of the preclinical promyelinating drugs clemastine and Sob-AM2 on KD OL pathologies using primary OLs isolated from the brains of twi mice. Both agents specifically prevented the apoptotic death observed in twi OLs. However, while Sob-AM2 showed higher efficacy in restoring the impaired differentiation and maturation of twi OLs, clemastine more potently reduced the endogenous psychosine levels. These results present the first preclinical in vitro data, suggesting that clemastine and Sob-AM2 can act directly and distinctly on OLs in KD and ameliorate their cellular pathologies associated with myelin degeneration.

A novel brain-penetrant oral UGT8 inhibitor decreases in vivo galactosphingolipid biosynthesis in murine Krabbe disease

Krabbe disease is a rare, inherited neurodegenerative disease due to impaired lysosomal β-galactosylceramidase (GALC) activity and formation of neurotoxic β-galactosylsphingosine ('psychosine'). We investigated substrate reduction therapy with a novel brain-penetrant inhibitor of galactosylceramide biosynthesis, RA 5557, in twitcher mice that lack GALC activity and model Krabbe disease. This thienopyridine derivative selectively inhibits uridine diphosphate-galactose glycosyltransferase 8 (UGT8), the final step in the generation of galactosylceramides which are precursors of sulphatide and, in the pathological lysosome, the immediate source of psychosine. Administration of RA 5557, reduced pathologically elevated psychosine concentrations (72-86%) in the midbrain and cerebral cortex in twitcher mice: the inhibitor decreased galactosylceramides by about 70% in midbrain and cerebral cortex in mutant and wild type animals. Exposure to the inhibitor significantly decreased several characteristic inflammatory response markers without causing apparent toxicity to myelin-producing cells in wild type and mutant mice; transcript abundance of oligodendrocyte markers MBP (myelin basic protein) and murine UGT8 was unchanged. Administration of the inhibitor before conception and during several breeding cycles to mice did not impair fertility and gave rise to healthy offspring. Nevertheless, given the unchanged lifespan, it appears that GALC has critical functions in the nervous system beyond the hydrolysis of galactosylceramide and galactosylsphingosine. Our findings support further therapeutic exploration of orally active UGT8 inhibitors in Krabbe disease and related galactosphingolipid disorders. The potent thienopyridine derivative with effective target engagement here studied appears to have an acceptable safety profile in vivo; judicious dose optimization will be needed to ensure efficacious clinical translation.

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.

Substrate reduction therapy for Krabbe disease and metachromatic leukodystrophy using a novel ceramide galactosyltransferase inhibitor

Krabbe disease (KD) and metachromatic leukodystrophy (MLD) are caused by accumulation of the glycolipids galactosylceramide (GalCer) and sulfatide and their toxic metabolites psychosine and lysosulfatide, respectively. We discovered a potent and selective small molecule inhibitor (S202) of ceramide galactosyltransferase (CGT), the key enzyme for GalCer biosynthesis, and characterized its use as substrate reduction therapy (SRT). Treating a KD mouse model with S202 dose-dependently reduced GalCer and psychosine in the central (CNS) and peripheral (PNS) nervous systems and significantly increased lifespan. Similarly, treating an MLD mouse model decreased sulfatides and lysosulfatide levels. Interestingly, lower doses of S202 partially inhibited CGT and selectively reduced synthesis of non-hydroxylated forms of GalCer and sulfatide, which appear to be the primary source of psychosine and lysosulfatide. Higher doses of S202 more completely inhibited CGT and reduced the levels of both non-hydroxylated and hydroxylated forms of GalCer and sulfatide. Despite the significant benefits observed in murine models of KD and MLD, chronic CGT inhibition negatively impacted both the CNS and PNS of wild-type mice. Therefore, further studies are necessary to elucidate the full therapeutic potential of CGT inhibition.

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.

Metabolic profiling reveals biochemical pathways and potential biomarkers associated with the pathogenesis of Krabbe disease

Krabbe disease (KD) is caused by mutations in the galactosylceramidase (GALC) gene, which encodes a lysosomal enzyme that degrades galactolipids, including galactosylceramide and galactosylsphingosine (psychosine). GALC deficiency results in progressive intracellular accumulation of psychosine, which is believed to be the main cause for the demyelinating neurodegeneration in KD pathology. Umbilical cord blood transplantation slows disease progression when performed presymptomatically but carries a significant risk of morbidity and mortality. Accurate presymptomatic diagnosis is therefore critical to facilitate the efficacy of existing transplant approaches and to avoid unnecessary treatment of children who will not develop KD. Unfortunately, current diagnostic criteria, including GALC activity, genetic analysis, and psychosine measurement, are insufficient for secure presymptomatic diagnosis. This study performs a global metabolomic analysis to identify pathogenetic metabolic pathways and novel biomarkers implicated in the authentic mouse model of KD known as twitcher. At a time point before onset of signs of disease, twitcher hindbrains had metabolic profiles similar to WT, with the exception of a decrease in metabolites related to glucose energy metabolism. Many metabolic pathways were altered after early signs of disease in the twitcher, including decreased phospholipid turnover, restricted mitochondrial metabolism of branched-chain amino acids, increased inflammation, and changes in neurotransmitter metabolism and osmolytes. Hypoxanthine, a purine derivative, is increased before signs of disease appear, suggesting its potential as a biomarker for early diagnosis of KD. Additionally, given the early changes in glucose metabolism in the pathogenesis of KD, diagnostic modalities that report metabolic function, such as positron emission tomography, may be useful in KD. © 2016 Wiley Periodicals, Inc.

Substrate reduction therapy for Krabbe's disease

Krabbe's disease (KD) is a lysosomal storage disorder in which galactosylceramide, a major glycosphingolipid of myelin, and psychosine (galactose-sphingosine) cannot be adequately metabolized because of a deficiency in galactosylceramidase. Substrate reduction therapy (SRT) has been tested in preclinical studies. The premise of SRT is to reduce the synthesis of substrates that are not adequately digested so that the substrate burden is lowered, resulting in less accumulation of unmetabolized material. SRT is used for Gaucher's disease, in which inhibitors of the terminal biosynthetic step are used. Unfortunately, an inhibitor for the final step of galactosylceramide biosynthesis, i.e., UDP glycosyltransferase 8 (a.k.a. UDP-galactose ceramide galactosyltransferase), has not been found. Approaches that inhibit an earlier biosynthetic step or that lessen the substrate burden by other means, such as genetic manipulations, have been tested in the twitcher mouse model of KD. Either as a stand-alone therapy or in combination with other approaches, SRT slowed the disease course, indicating that this approach has potential therapeutic value. For instance, in individuals with adult-onset disease, SRT theoretically could lessen the production of substrates so that residual enzymatic activity could adequately manage the lower substrate burden. In more severe forms of disease, SRT theoretically could be part of a combination therapy. However, SRT has the potential to impair normal function by reducing the synthesis of galactosylceramide to levels that impede myelin function, or SRT could have other deleterious effects. Thus, multiple issues need to be resolved before this approach is ready for testing in humans. © 2016 Wiley Periodicals, Inc.

Bio-recognition and functional lipidomics by glycosphingolipid transfer technology

Through glycosphingolipid biochemical research, we developed two types of transcription technologies. One is a biochemical transfer of glycosphingolipids to peptides. The other is a physicochemical transfer of glycosphingolipids in silica gel to the surface of a plastic membrane. Using the first technology, we could prepare peptides which mimic the shapes of glycosphingolipid molecules by biopanning with a phage-displayed peptide library and anti-glycosphingolipid antibodies as templates. The peptides thus obtained showed biological properties and functions similar to those of the original glycosphingolipids, such as lectin binding, glycosidase modulation, inhibition of tumor metastasis and immune response against the original antigen glycosphingolipid, and we named them glyco-replica peptides. The results showed that the newly prepared peptides could be used effectively as a bio-recognition system and suggest that the glyco-replica peptides can be widely applied to therapeutic fields. Using the second technology, we could establish a functional lipidomics with a thin-layer chromatography-blot/matrix-assisted laser desorption ionization-time of flight mass spectrometry (TLC-Blot/MALDI-TOF MS) system. By transferring glycosphingolipids on a plastic membrane surface from a TLC plate, innovative biochemical approaches such as simple purification of individual glycosphingolipids, binding studies, and enzyme reactions could be developed. The combinations of these biochemical approaches and MALDI-TOF MS on the plastic membrane could provide new strategies for glycosphingolipid science and the field of lipidomics. In this review, typical applications of these two transfer technologies are introduced.(Communicated by Kunihiko SUZUKI, M.J.A.).

Kunihiko Suzuki and sphingolipidoses

Kunihiko Suzuki is a neurologist by training whose research accomplishments range widely from basic research in brain lipids, their metabolism to genetic disorders involving the nervous system. Among them are identification of the enzymatic defect, the pathogenetic mechanism, and animal models of Krabbe's globoid cell leukodystrophy, the chemical and molecular pathologies of many glycosphingolipidoses, discovery of the abnormal accumulation of very long chain fatty acids in adrenoleukodystrophy, and elucidation of the complex metabolic interrelationship among sphingolipids with extensive use of the gene targeting technology. This reflections and perspectives highlight his accomplishments briefly.

Functional roles of gangliosides in neurodevelopment: an overview of recent advances

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nervous system. They are localized primarily in the outer leaflets of plasma membranes and participated in cell-cell recognition, adhesion, and signal transduction and are integral components of cell surface microdomains or lipid rafts along with proteins, sphingomyelin and cholesterol. Ganglioside-rich lipid rafts play an important role in signaling events affecting neural development and the pathogenesis of certain diseases. Disruption of gangloside synthase genes in mice induces developmental defects and neural degeneration. Targeting ganglioside metabolism may represent a novel therapeutic strategy for intervention in certain diseases. In this review, we focus on recent advances on metabolic and functional studies of gangliosides in normal brain development and in certain neurological disorders.

Functions of sphingolipid metabolism in mammals--lessons from genetic defects

Much is known about the pathways that control the biosynthesis, transport and degradation of sphingolipids. During the last two decades, considerable progress has been made regarding the roles this complex group of lipids play in maintaining membrane integrity and modulating responses to numerous signals. Further novel insights have been provided by the analysis of newly discovered genetic diseases in humans as well as in animal models harboring mutations in the genes whose products control sphingolipid metabolism and action. Through the description of the phenotypic consequences of genetic defects resulting in the loss of activity of the many proteins that synthesize, transport, bind, or degrade sphingolipids, this review summarizes the (patho)physiological functions of these lipids.

Sphingolipids and membrane biology as determined from genetic models

The importance of sphingolipids in membrane biology was appreciated early in the twentieth century when several human inborn errors of metabolism were linked to defects in sphingolipid degradation. The past two decades have seen an explosion of information linking sphingolipids with cellular processes. Studies have unraveled mechanistic details of the sphingolipid metabolic pathways, and these findings are being exploited in the development of novel therapies, some now in clinical trials. Pioneering work in yeast has laid the foundation for identifying genes encoding the enzymes of the pathways. The advent of the era of genomics and bioinformatics has led to the identification of homologous genes in other species and the subsequent creation of animal knock-out lines for these genes. Discoveries from these efforts have re-kindled interest in the role of sphingolipids in membrane biology. This review highlights some of the recent advances in understanding sphingolipids' roles in membrane biology as determined from genetic models.

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.

Neural transplantation of human MSC and NT2 cells in the twitcher mouse model

BACKGROUND

Accumulating evidence has demonstrated that the NT2 embryonal carcinoma cell line and multipotential stem cells found in BM, mesenchymal stromal cells (MSC), have the ability to differentiate into a wide variety of cell types. This study was designed to explore the efficacy of these two human stem cell types as a graft source for the treatment of demyelinating disorders such as Krabbe's disease and multiple sclerosis (MS).

METHODS

We examined the engraftment and in vivo differentiation of adult MSC and NT2 cells after transplantation into two demyelinating environments, the neonatal and postnatal twitcher mouse brain.

RESULTS

Both types of xenografts led to anatomical integration, without tumor formation, and remained viable in the normal and twitcher mouse brain, showing differentiation into neurons, astrocytes and oligodendrocytes.

DISCUSSION

This study represents a platform for further stem cell transplantation studies in the twitcher model and potentially has important therapeutic implications.

Sphingolipid metabolism diseases

Human diseases caused by alterations in the metabolism of sphingolipids or glycosphingolipids are mainly disorders of the degradation of these compounds. The sphingolipidoses are a group of monogenic inherited diseases caused by defects in the system of lysosomal sphingolipid degradation, with subsequent accumulation of non-degradable storage material in one or more organs. Most sphingolipidoses are associated with high mortality. Both, the ratio of substrate influx into the lysosomes and the reduced degradative capacity can be addressed by therapeutic approaches. In addition to symptomatic treatments, the current strategies for restoration of the reduced substrate degradation within the lysosome are enzyme replacement therapy (ERT), cell-mediated therapy (CMT) including bone marrow transplantation (BMT) and cell-mediated "cross correction", gene therapy, and enzyme-enhancement therapy with chemical chaperones. The reduction of substrate influx into the lysosomes can be achieved by substrate reduction therapy. Patients suffering from the attenuated form (type 1) of Gaucher disease and from Fabry disease have been successfully treated with ERT.

Oligodendrocyte-specific ceramide galactosyltransferase (CGT) expression phenotypically rescues CGT-deficient mice and demonstrates that CGT activity does not limit brain galactosylceramide level

Galactosylceramide (GalC) is the major sphingolipid of the myelin membrane. Mice lacking GalC due to ceramide galactosyltransferase (CGT) deficiency form unstable and functionally affected myelin and exhibit a progressive demyelination, accompanied by severe motor coordination deficits. In addition to oligodendrocytes, CGT is also expressed in other cells, e.g., neurons and astrocytes. We examined the possibility that lack of CGT in these cells contributes to the phenotype of CGT-deficient mice. Toward this aim, we generated transgenic mice expressing CGT under the control of oligodendrocyte-specific proteolipid protein (PLP) promoter and examined the possibility of a transgenic rescue of CGT-deficient mice. CGT-deficient mice expressing the PLP-CGT transgene did not show any behavioral abnormalities, normal myelin structure, and MBP levels. CGT activity as well as GalC and sulfatide levels of rescued mice were not significantly different from wild-type controls. Thus, transgenic rescue with the PLP-CGT transgene was apparently complete. In contrast to wild-type and rescued mice, PLP-CGT transgenic mice on a wild-type background exhibited significantly elevated CGT activity which directly correlated with an increase in non-hydroxy fatty acid (NFA)-GalC, but not alpha-hydroxy fatty acid (HFA)-GalC. HFA-GalC decreased in adult transgenic mice, indicating that NFA-GalC, but not HFA-GalC levels are limited by CGT activity. As a consequence, the total amount of GalC is unchanged over a rather wide range of CGT expression levels in the mouse brain. Our results indicate that loss of CGT in oligodendrocytes is exclusively responsible for the myelin structural deficits, demyelination, and behavioral abnormalities in CGT-deficient mice.

Paranodal transverse bands are required for maintenance but not initiation of Nav1.6 sodium channel clustering in CNS optic nerve axons

The rapid, efficient, and faithful propagation of action potentials in myelinated nerve fibers depends on the appropriate complement and localization of ion channels. Recent work has suggested that specific voltage-dependent sodium (Nav) channel isoforms are differentially regulated both spatially and temporally in a myelin-dependent manner. Since the principal site of axoglial contact occurs at the paranode, we postulated that disrupted paranodal structure might result in altered nodal Nav channel isoform localization and clustering. We have used UDP-galactose/ceramide galactosyl transferase (CGT)-deficient mice, which form compact myelin and paranodal loops but lack the transverse bands normally found at the interface of the axon and overlying glial cell, to determine if this structure contributes to the signaling machinery responsible for clustering and localization of distinct Nav channel isoforms. We find that as in control animals, most mutant nodes of Ranvier had Nav1.6 in high-density clusters in the peripheral and central nervous systems; the localization of Nav1.2 and the protein levels of Nav1.2 and Nav1.6 were also normal in the CGT-deficient mouse. However, with increasing age, in the mutant mouse we observed a decrease in the total number of nodal Nav1.6 clusters, a decrease in the density of Nav1.6 channels at nodes, and an increase in the average size of the Nav1.6 clusters. Thus, transverse bands are not required for Nav1.6 clustering and localization at nodes or for exclusion of Nav1.2 from myelinated nerve fibers, but are required for the maintenance of nodal Nav1.6 cluster size and density.

Are animal models useful for understanding the pathophysiology of lysosomal storage disease?

Spontaneously occurring genetic lysosomal storage diseases are as rare in other mammalian species as in man. However, the advent of gene targeting technology has revolutionized the state of animal models of genetic diseases. Nearly all lysosomal storage diseases known in man have been duplicated in the mouse. The technology now allows, not only complete inactivation of endogenous genes, but also the introduction of essentially any type of mutation. These animal models can overcome many of the limitations inherent in studies of human patients--rarity of the disease, extremely complex genetic background and logistical and ethical constraints in the design and execution of experiments with human subjects. For example, genetic manipulations of germ cells or cross-breeding experiments between two mutants are readily feasible with animal models. Two major areas of the utility of animal models are the clarification of the pathophysiology/pathogenetic mechanism of disease and the exploration of therapeutic approaches. Examples of experiments using animal models of lysosomal storage disease are presented, primarily from studies undertaken in our own laboratory.

CONCLUSION

Animal models have proved invaluable in extending our knowledge of the lysosomal storage diseases and exploring potential therapies.

Globoid cell leukodystrophy (Krabbe's disease): update

The classic globoid cell leukodystrophy (Krabbe's disease) is caused by genetic defects in a lysosomal enzyme, galactosylceramidase. It is one of the two classic genetic leukodystrophies, together with metachromatic leukodystrophy. The mode of inheritance is autosomal recessive. Typically, the disease occurs among infants and takes a rapidly fatal course, but rarer late-onset forms also exist. Clinical manifestations are exclusively neurologic with prominent white-matter signs. The pathology is unique, consisting of a rapid and nearly complete disappearance of myelin and myelin-forming cells--the oligodendrocytes in the central nervous system and the Schwann cells in the peripheral nervous system, reactive astroytic gliosis, and infiltration of the unique and often multinucleated macrophages ("globoid cells") that contain strongly periodic acid-Schiff (PAS)-positive materials. A normally insignificant but highly cytotoxic metabolite, galactosylsphingosine (psychosine), is also a substrate of galactosylceramidase and is considered to play a critical role in the pathogenesis. The galactosylceramidase gene has been cloned, and a large number of disease-causing mutations have been identified. Equivalent genetic galactosylceramidase deficiency occurs in several mammalian species, such as mouse, dog, and monkey. Recently, deficiency of one of the sphingolipid activator proteins, saposin A, was demonstrated to cause a late-onset, slowly progressive globoid cell leukodystrophy at least in the mouse, with all of the phenotypic consequences of impaired degradation of galactosylceramidase substrates. Human globoid cell leukodystrophy owing to saposin A deficiency might be anticipated and should be suspected in human patients with a late-onset leukodystrophy with normal galactosylceramidase activity when other possibilities are also excluded. The only serious attempt at treating human patients is bone marrow transplantation, which can provide significant alleviation of symptoms, particularly in those patients with later-onset, more slowly progressive globoid cell leukodystrophy.

Substrate-reduction therapy enhances the benefits of bone marrow transplantation in young mice with globoid cell leukodystrophy

Globoid cell leukodystrophy is an autosomal recessive disease with progressive demyelination caused by a deficiency of the lysosomal enzyme galactosylceramidase. Bone marrow transplantation (BMT) is a therapeutic option for patients with late-onset disease and for patients with early onset disease that had an early diagnosis owing to an affected sibling. This therapy, however, typically is not effective for early onset disease when the diagnosis occurs after several months of life. In an effort to enable a broader range of patients to benefit from BMT, we tested whether combining substrate-reduction therapy with BMT would result in a greater benefit than either treatment alone in the twitcher mouse model of globoid cell leukodystrophy. Twitcher mice treated with L-cycloserine, an inhibitor of 3-ketodyhydrosphingosine synthase, and transplanted with 50 +/- 5 x 10(6) bone marrow cells on d 10 had a mean life-span of 112 d compared with 51 d for BMT alone (p < 0.001) or L-cycloserine alone, which was previously reported to be 56 d. L-Cycloserine treatment also was initiated neonatally to determine whether it would allow for a delayed BMT to have therapeutic value. Twitcher mice given only BMT at 18 d or only a short course of L-cycloserine died at 36 and 37 d, respectively. Twitcher mice given a short course of L-cycloserine + BMT at 18 d lived to 58 d (p = 0.0006). In conclusion, substrate-reduction therapy enhanced the value of BMT in twitcher mice, suggesting that this combination strategy might benefit patients with globoid cell leukodystrophy.

Expression of immune-related molecules is downregulated in twitcher mice following bone marrow transplantation

Twitcher (twi/twi) is a murine model of a human genetic demyelinating disease, globoid cell leukodystrophy (Krabbe disease). The affected mice usually die before reaching age 45 days, having demyelination associated with extensive glial activation. The twi/twi mice that receive wild-type bone marrow transplantation (BMT) survive up to 3 times longer with improved pathology. We hypothesize that immune-related molecules such as cytokines and chemokines are partly responsible for the demyelination in twi/twi, and that the decrease in the expression of such molecules following BMT contributes to clinico-pathological improvement. Cells expressing TNF-alpha, MCP-1, and MIP-1beta were conspicuous in the twi/twi CNS accompanied by infiltration of Ia+ and CD8+/CD3- hematogenous cells. These cells decreased gradually after BMT TNF-alpha mRNA and mRNA of C-C chemokine families, including MCP-1, IP-10, MIP-1alpha, MIP-1beta, and RANTES, were upregulated in the twi/twi CNS but downregulated gradually following BMT. In twi/twi that survived to 20 wk of age, cells expressing TNF-alpha, MCP-1, MIP-1beta, Ia, or CD8 were hardly detected and pathology was clearly improved. These results are consistent with the hypothesis that cytokine expression in glial cells contributes (to some extent) to the pathogenesis of demyelinating lesions in the twi/twi mice.

Leukodystrophies: recent developments in genetics, molecular biology, pathogenesis and treatment

The combined application of recently developed techniques for genetic and biochemical analysis, neuroimaging and the ability to create animal models has led to remarkable advances in the field of leukodystrophy research. The present review focuses on recent developments in X-linked adrenoleukodystrophy, Alexanders disease, Canavans disease, metachromatic leukodystrophy, globoid cell leukodystrophy (Krabbes disease) and Pelizaeus-Merzbacher disease, and briefly discusses new data on six other rare inherited leukodystrophies. Of the leukodystrophies, 12 can now be diagnosed precisely using noninvasive techniques, and the molecular defect has been identified in nine of these. Disease incidence can be reduced through genetic counselling. Presymptomatic diagnosis provides an opportunity for therapeutic intervention. Study of animal models facilitates elucidation of pathogenic mechanisms and identifies pathways that could be targeted by future therapies.

Requirement of seminolipid in spermatogenesis revealed by UDP-galactose: Ceramide galactosyltransferase-deficient mice

Although seminolipid has long been suspected to play an essential role in spermatogenesis because of its uniquely abundant and temporally regulated expression in the spermatocytes, direct experimental evidence has been lacking. We have tested the hypothesis by examining the testis of the UDP-galactose:ceramide galactosyltransferase-deficient mouse, which is incapable of synthesizing seminolipid. Spermatogenesis in homozygous affected males is arrested at the late pachytene stage and the spermatogenic cells degenerate through the apoptotic process. This stage closely follows the phase of rapid seminolipid synthesis in the wild-type mouse. These observations not only provide the first experimental evidence that seminolipid is indeed essential for normal spermatogenesis but also support the broader concept that cell surface glycolipids are important in cellular differentiation and cell-to-cell interaction.

Distribution and characterization of GFP(+) donor hematogenous cells in Twitcher mice after bone marrow transplantation

The twitcher mouse is a murine model of globoid cell leukodystropy, a genetic demyelinating disease caused by a mutation of the galactosylceramidase gene. Demyelination of the central nervous system commences around 20 postnatal days. Using GFP-transgenic mice as donors, the distribution of hematogenous cells after bone marrow transplantation was investigated in the twitcher mice. Bone marrow transplantation was carried out at 8 postnatal days. In twitcher chimeric mice examined before 30 postnatal days, numerous GFP(+) cells were detected in spleen and peripheral nerve but only a few were detected in the liver, lung, and spinal white matter. In contrast, at 35 to 40 postnatal days when demyelination is evident, many GFP(+) cells with ameboid form were detected in the white matter of the spinal cord, brainstem, and cerebrum. Approximately half of these GFP(+) cells were co-labeled with Mac-1. In twitcher chimeric mice examined after 100 postnatal days, the majority of GFP/Mac-1 double-positive cells displayed the morphological features of ramified microglia with fine delicate processes and was distributed diffusely in both gray and white matter. These results suggest that a significant number of donor hematogenous cells are able to infiltrate into the brain parenchyma, repositioning themselves into areas previously occupied by microglia, and to ameliorate lethality.