Masako Taniike

Molecular cloning and expression of cDNA for murine galactocerebrosidase and mutation analysis of the twitcher mouse, a model of Krabbe's disease

Abstract: The cDNA for a murine galactocerebrosidase was isolated from a murine testis cDNA library on the basis of its homology with the cDNA for human galactocerebrosidase and a PCR method was used to clone the 5′ end. It has a 2,278‐nucleotide sequence including a 2,004‐nucleotide open reading frame, which encodes 668 amino acid residues. The identity between the human and murine amino acid sequences was very high, being calculated to be 84%. Sequencing of cDNA from liver of the twitcher mouse revealed a nonsense mutation at codon 339 (TGG → TGA). The most abundant mRNA of the murine galactocerebrosidase gave a 3.6‐kb band, which was not detected in twitcher mice. This suggests that the cDNA (2,278 bp) we characterized represents a minor species generated by an alternate poly(A) signal and that most of the mRNA has a much longer 3′‐untranslated region. Genome analysis revealed that this mutation was homozygous in the twitcher and heterozygous in the carrier but was not present in normal mice. The normal mouse cDNA but not the mutant cDNA of the galactocerebrosidase transfected into COS1 cells gave rise to an increase in enzymatic activity. We concluded that this mutation results in the deficiency of galactocerebrosidase in the twitcher mouse.

Two genetic variants of CD38 in subjects with autism spectrum disorder and controls.

The neurobiological basis of autism spectrum disorder (ASD) remains poorly understood. Given the role of CD38 in social recognition through oxytocin (OT) release, we hypothesized that CD38 may play a role in the etiology of ASD. Here, we first examined the immunohistochemical expression of CD38 in the hypothalamus of post-mortem brains of non-ASD subjects and found that CD38 was colocalized with OT in secretory neurons. In studies of the association between CD38 and autism, we analyzed 10 single nucleotide polymorphisms (SNPs) and mutations of CD38 by re-sequencing DNAs mainly from a case-control study in Japan, and Caucasian cases mainly recruited to the Autism Genetic Resource Exchange (AGRE). The SNPs of CD38, rs6449197 (p<0.040) and rs3796863 (p<0.005) showed significant associations with a subset of ASD (IQ>70; designated as high-functioning autism (HFA)) in the U.S. 104 AGRE family trios, but not with Japanese 188 HFA subjects. A mutation that caused tryptophan to replace arginine at amino acid residue 140 (R140W; (rs1800561, 4693C>T)) was found in 0.6-4.6% of the Japanese population and was associated with ASD in the smaller case-control study. The SNP was clustered in pedigrees in which the fathers and brothers of T-allele-carrier probands had ASD or ASD traits. In this cohort OT plasma levels were lower in subjects with the T allele than in those without. One proband with the T allele who was taking nasal OT spray showed relief of symptoms. The two variant CD38 poloymorphysms tested may be of interest with regard of the pathophysiology of ASD.

Prostaglandin D2-Mediated Microglia/Astrocyte Interaction Enhances Astrogliosis and Demyelination in twitcher

Prostaglandin (PG) D2 is well known as a mediator of inflammation. Hematopoietic PGD synthase (HPGDS) is responsible for the production of PGD2 involved in inflammatory responses. Microglial activation and astrogliosis are commonly observed during neuroinflammation, including that which occurs during demyelination. Using the genetic demyelination mouse twitcher, a model of human Krabbe’s disease, we discovered that activated microglia expressed HPGDS and activated astrocytes expressed the DP1 receptor for PGD2 in the brain of these mice. Cultured microglia actively produced PGD2 by the action of HPGDS. Cultured astrocytes expressed two types of PGD2 receptor, DP1 and DP2, and showed enhanced GFAP production after stimulation of either receptor with its respective agonist. These results suggest that PGD2 plays an important role in microglia/astrocyte interaction. We demonstrated that the blockade of the HPGDS/PGD2/DP signaling pathway using HPGDS- or DP1-null twitcher mice, and twitcher mice treated with an HPGDS inhibitor, HQL-79 (4-benzhydryloxy-1-[3-(1H-tetrazol-5-yl)-propyl]piperidine), resulted in remarkable suppression of astrogliosis and demyelination, as well as a reduction in twitching and spasticity. Furthermore, we found that the degree of oligodendroglial apoptosis was also reduced in HPGDS-null and HQL-79-treated twitcher mice. These results suggest that PGD2 is the key neuroinflammatory molecule that heightens the pathological response to demyelination in twitcher mice.

Lipocalin-type prostaglandin D synthase/β-trace is a major amyloid β-chaperone in human cerebrospinal fluid

The conformational change in amyloid β (Aβ) peptide from its monomeric form to aggregates is crucial in the pathogenesis of Alzheimers disease (AD). In the healthy brain, some unidentified chaperones appear to prevent the aggregation of Aβ. Here we reported that lipocalin-type prostaglandin D synthase (L-PGDS)/β-trace, the most abundant cerebrospinal fluid (CSF) protein produced in the brain, was localized in amyloid plaques in both AD patients and AD-model Tg2576 mice. Surface plasmon resonance analysis revealed that L-PGDS/β-trace tightly bound to Aβ monomers and fibrils with high affinity (KD = 18–50 nM) and that L-PGDS/β-trace recognized residues 25–28 in Aβ, which is the key region for its conformational change to a β-sheet structure. The results of a thioflavin T fluorescence assay to monitor Aβ aggregation disclosed that L-PGDS/β-trace inhibited the spontaneous aggregation of Aβ (1–40) and Aβ (1–42) within its physiological range (1–5 μM) in CSF. L-PGDS/β-trace also prevented the seed-dependent aggregation of 50 μM Aβ with Ki of 0.75 μM. Moreover, the inhibitory activity toward Aβ (1–40) aggregation in human CSF was decreased by 60% when L-PGDS/β-trace was removed from the CSF by immunoaffinity chromatography. The deposition of Aβ after intraventricular infusion of Aβ (1–42) was 3.5-fold higher in L-PGDS-deficient mice and reduced to 23% in L-PGDS-overexpressing mice as compared with their wild-type levels. These data indicate that L-PGDS/β-trace is a major endogenous Aβ-chaperone in the brain and suggest that the disturbance of this function may be involved in the onset and progression of AD. Our findings may provide a diagnostic and therapeutic approach for AD.

An Apoptotic Depletion of Oligodendrocytes in the Twitcher, a Murine Model of Globoid Cell Leukodystrophy

Morphological alterations of oligodendrocytes (OLs) leading to their depletion were studied in the genetic demyelinating mutant, twitcher, a murine model of globoid cell leukodystrophy (GLD). With pi-glutathione-S-transferase immunostaining, OLs with multiple varicose processes were recognized in the early stages and adjacent areas of demyelination and then the OLs cytoplasm as well as the processes became shrunken with progression of the disease. These shrunken OLs were labeled by the TUNEL method, indicative of apoptotic cell death. The ultrastructural features of apoptotic cells were noted in these OLs and DNA laddering was noted in the twitcher brain in advanced stages. This is the first report describing the gradual depletion of OLs by apoptosis in genetic demyelination.

Long-Term Administration of Intranasal Oxytocin Is a Safe and Promising Therapy for Early Adolescent Boys with Autism Spectrum Disorders

OBJECTIVE Oxytocin (OT) has been a candidate for the treatment of autism spectrum disorders (ASD), and the impact of intranasally delivered OT on ASD has been investigated. However, most previous studies were conducted by single-dose administration to adults; and, therefore, the long-term effect of nasal OT on ASD patients and its effect on children remain to be clarified. METHODS We conducted a singled-armed, open-label study in which OT was administered intranasally over the long term to eight male youth with ASD (10-14 years of age; intelligence quotient [IQ] 20-101). The OT administration was performed in a stepwise increased dosage manner every 2 months (8, 16, 24 IU/dose). A placebo period (1-2 weeks) was inserted before each step. The outcome measures were autism diagnostic observation schedule--generic (ADOS-G), child behavior checklist (CBCL), and the aberrant behavior checklist (ABC). In addition, side effects were monitored by measuring blood pressure and examining urine and blood samples. RESULTS Six of the eight participants showed improved scores on the communication and social interaction domains of the ADOS-G. However, regarding the T-scores of the CBCL and the scores of the ABC, we could not find any statistically significant improvement, although several subcategories showed a mild tendency for improvement. Caregivers of five of the eight participants reported certain positive effects of the OT therapy, especially on the quality of reciprocal communication. All participants showed excellent compliance and no side effects. CONCLUSIONS Although our results on the efficacy of long-term nasal OT therapy still remain controversial, to the best of our knowledge, this is the first report documenting the safety of long-term nasal OT therapy for children with ASD. Even though our data are too preliminary to draw any definite conclusions about efficacy, they do suggest this therapy to be safe, promising, and worthy of a large-scale, double-blind placebo-controlled study.

Clinical phenotype and endocrinological investigations in a patient with a mutation in the MCT8 thyroid hormone transporter

Thyroid hormones are known to be essential for growth, development, and metabolism. Recently, the monocarboxylate transporter 8 (MCT8) was identified as a thyroid hormone transporter, and MCT8 mutations have been associated with Allan-Herndon-Dudley syndrome, an X linked condition characterized by severe mental retardation, dysarthria, athetoid movements, muscle hypoplasia, and spastic paraplegia. Here we describe in detail the clinical and biochemical features and the response to thyroid hormone (L-thyroxine (LT4)) administration in a boy with an MCT8 mutation (c.1649delA) that truncates the protein in the twelfth transmembrane domain. It is of note that brain magnetic resonance imaging (MRI) revealed delayed myelination from infancy. Endocrine functions other than thyroid hormone regulation and metabolism were intact, resulting in normal hypothalamic/pituitary function tests. While LT4 administration suppressed thyrotropin (TSH) secretion, no significant changes in thyroid hormone values or clinical symptoms were observed. Conclusion: the characteristic thyroid hormone function tests and brain MRI findings may allow screening of high-risk populations for a better understanding of MCT8 pathophysiology.

Prostaglandin D2 Protects Neonatal Mouse Brain from Hypoxic Ischemic Injury

Prostaglandin D2 (PGD) is synthesized by hematopoietic PGD synthase (HPGDS) or lipocalin-type PGDS (L-PGDS), depending on the organ in which it is produced, and binds specifically to either DP1 or DP2 receptors. We investigated the role of PGD2 in the pathogenesis of hypoxic-ischemic encephalopathy (HIE) in neonatal mice at postnatal day 7. In wild-type mice, hypoxia-ischemia increased PGD2 production in the brain up to 90-fold compared with the level in sham-operated brains at 10 min after cessation of hypoxia. Whereas the size of the infarct was not changed in L-PGDS or DP2 knock-out mouse brains compared with that in the wild-type HIE brains, it was significantly increased in HPGDS–L-PGDS double knock-out or DP1 knock-out mice. The PGD2 level in L-PGDS, HPGDS, and HPGDS–L-PGDS knock-out mice at 10 min of reoxygenation was 46, 7, and 1%, respectively, of that in the wild-type ones, indicating the infarct size to be in inverse relation to the amount of PGD2 production. DP1 receptors were exclusively expressed in endothelial cells after 1 h of reoxygenation, and cerebral blood flow decreased more rapidly after the onset of hypoxia and did not return to the baseline level after reoxygenation in HPGDS–L-PGDS knock-out mice. Endothelial cells were severely damaged in HPGDS–L-PGDS and DP1 knock-out mice after 1 h of reoxygenation. In the human neonatal HIE brain, HPGDS-positive microglia were increased in number. In conclusion, it is probable that PGD2 protected the neonatal brain from hypoxic-ischemic injury mainly via DP1 receptors by preventing endothelial cell degeneration.

Mitochondrial encephalomyopathies with the mutation of the mitochondrial tRNALeu(UUR) gene

Four families with mitochondrial encephalomyopathy are described. Probands of three families had typical clinical presentations of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS), but the proband of family 4 lacked strokelike episodes. The mitochondrial DNA mutation of tRNA(Leu(UUR)) (transfer ribonucleic acid specific to leucine (UUR codon)) found in MELAS was examined in muscle DNA obtained from biopsy samples of the probands of four families and the maternal relatives of family 2. The mutation was detected in all muscle samples, and the degree of the mutated DNA was 68% to 84% by Southern blot analysis. However, the clinical patterns of the maternal relatives of family 2 were mild and distinctly different from MELAS. The same mutation was also detected in blood-derived DNA samples of all family members examined, including healthy mothers but not fathers, although the degree of mutation did not correlate with the clinical severity. These results confirmed the maternal inheritance of this disease and suggested that the mitochondrial DNA mutation (tRNA(Leu(UUR))) may cause clinical symptoms other than MELAS. The clinical findings of mitochondrial encephalomyopathy should be reinvestigated in terms of the mitochondrial gene mutation; the polymerase chain reaction method will be useful for screening for this mutation of mitochondrial DNA in blood samples.

Six novel mutations detected in the GALC gene in 17 Japanese patients with Krabbe disease, and new genotype–phenotype correlation

AbstractKrabbe disease is an autosomal recessive leukodystrophy. It is pathologically characterized by demyelination of the central and peripheral nervous systems and the accumulation of globoid cells in brain white matter. It is caused by a deficiency of galactocerebrosidase (GALC) activity. We investigated mutations of the GALC gene in 17 Japanese patients with Krabbe disease, the largest subject number of Japanese patients to date, and found 27 mutations. Of these mutations, six were novel, including two nonsense mutations, W115X and R204X, two missense mutations, S257F and L364R, a small deletion, 393delT, and a small insertion, 1719-1720insT. Our findings, taken with the reported mutations in Japanese patients, confirm several mutations common to Japanese patients, the two most frequent being 12Del3Ins and I66M+I289V, which account for 37% of all mutant alleles. With two additional mutations, G270D and T652P, these account for up to 57% of genetic mutations in Japanese patients. Distribution of the mutations within the GALC gene indicated some genotype-phenotype correlation. I66M+I289M, G270D, and L618S contributed to a mild phenotype. Screening for these mutations may provide an effective method with which to predict the clinical phenotype.