Biomedical subjects

Tsuyoshi Tahara

Publications and source records attributed to Tsuyoshi Tahara.

5 recordsLinked to original sources

PubMed2006

Decrease of hepatic delta-aminolevulinate dehydratase activity in an animal model of fatigue.

Fatigue can be defined physiologically as inability to maintain the expected power output. At present, no standard of fatigue are yet available. In order to find biomarkers of fatigue, we investigated the level of delta-aminolevulinic acid (ALA), the first intermediate metabolite in the heme biosynthetic pathway, in the plasma and urine of an animal model of fatigue. To prepare fatigued animals, we kept rats for 5 days in a cage filled with water to a height of 1.5 cm. As a result, the plasma and urinary ALA levels were increased in the fatigued animals as compared with those in the control animals. One day after the rats had been returned to their normal cages, these increased levels were restored to the control ones. We also examined the activity of the enzyme ALA dehydratase (ALAD), which is the second enzyme in the heme biosynthetic pathway, and ALAD gene expression during the fatigue and its recovery sessions. The ALAD activity, as well as its gene expression, in the liver of the fatigued animals was decreased as compared with those of the control animals. Both activity and gene expression of ALAD were recovered to their respective control levels after the rats had been allowed to rest in their normal cages for 1 day. Furthermore, the activity of ALA synthase (ALAS), the rate-limiting enzyme in the heme biosynthesis, in the liver was increased after the fatigue session for 5 days. Although this level of increase in the plasma concentration of ALA may not induce fatigue, increase in plasma and urinary ALA levels can be biomarkers of fatigue.

5-Aminolevulinate Synthetase↗

PubMed2006

Dual gene defects involving delta-aminolaevulinate dehydratase and coproporphyrinogen oxidase in a porphyria patient.

Summary A Caucasian male had symptoms of acute porphyria, with increases in urinary delta-aminolaevulinic acid (ALA), porphobilinogen (PBG) and coproporphyrin that were consistent with hereditary coproporphyria (HCP). However, a greater than expected increase in ALA, compared with PBG, and a substantial increase in erythrocyte zinc protoporphyrin, suggested additional ALA dehydratase (ALAD) deficiency. Nucleotide sequence analysis of coproporphyrinogen oxidase (CPO) cDNA of the patient, but not of the parents, revealed a novel nucleotide transition G835-->C, resulting in an amino acid change, G279R. The mutant CPO protein expressed in Escherichia coli was unstable, and produced about 5% of activity compared with the wild-type CPO. Erythrocyte ALAD activity was 32% of normal in the proband. Nucleotide sequence analysis of cloned ALAD cDNAs from the patient revealed a C36-->G base transition (F12L amino acid change). The F12L ALAD mutation, which was found in the mother and a brother, was previously described, and is known to lack any enzyme activity. This patient thus represents the first case of porphyria where both CPO and ALAD deficiencies were demonstrated at the molecular level.

Adult↗

PubMed2004

Heme-dependent up-regulation of the alpha-globin gene expression by transcriptional repressor Bach1 in erythroid cells.

The transcriptional factor Bach1 forms a heterodimer with small Maf family, and functions as a repressor of the Maf recognition element (MARE) in vivo. To investigate the involvement of Bach1 in the heme-dependent regulation of the expression of the alpha-globin gene, human erythroleukemia K562 cells were cultured with succinylacetone (SA), a heme biosynthetic inhibitor, and the level of alpha-globin mRNA was examined. A decrease of alpha-globin mRNA was observed in SA-treated cells, which was restored by the addition of hemin. The heme-dependent expression of alpha-globin occurred at the transcriptional level since the expression of human alpha-globin gene promoter-reporter gene containing hypersensitive site-40 (HS-40) was decreased when K562 cells were cultured with SA. Hemin treatment restored the decrease of the promoter activity by SA. The regulation of the HS-40 activity by heme was dependent on the NF-E2/AP-1 (NA) site, which is similar to MARE. The NA site-binding activity of Bach1 in K562 increased upon SA-treatment, and the increase was diminished by the addition of hemin. The transient expression of Bach1 and mutated Bach1 lacking CP motifs suppressed the HS-40 activity, and cancellation of the repressor activity by hemin was observed when wild-type Bach1 was expressed. The expression of NF-E2 strengthened the restoration of the Bach1-effect by hemin. Interestingly, nuclear localization of Bach1 increased when cells were treated with SA, while hemin induced the nuclear export of Bach1. These results indicated that heme plays an important role in the induction of alpha-globin gene expression through disrupting the interaction of Bach1 and the NA site in HS-40 enhancer in erythroid cells.

Animals↗

PubMed2003

Heme positively regulates the expression of beta-globin at the locus control region via the transcriptional factor Bach1 in erythroid cells.

The transcription factor Bach1 heterodimerizes with small Maf proteins to repress Maf recognition element (MARE)-dependent gene expression. The repressor activity of Bach1 is inhibited by the direct binding of heme. To investigate the involvement of Bach1 in the heme-dependent regulation of the expression of the beta-globin gene, mouse erythroleukemia (MEL) cells were cultured with succinylacetone (SA), a specific inhibitor of heme biosynthesis, and the level of beta-globin mRNA was examined. A marked decrease of beta-globin mRNA in SA-treated cells was observed, and this decrease was reversed by the addition of hemin. An iron chelator, desferrioxamine, also lowered the level of beta-globin mRNA. The heme-dependent expression of beta-globin is a transcriptional event since the expression of the human beta-globin gene promoter-reporter gene containing the microlocus control region (microLCR) was inhibited when human erythroleukemia K562 cells and MEL cells were cultured with SA. Hemin treatment restored the decrease in promoter activity caused by SA. The control of the microLCR-beta-globin promoter reporter gene by heme was dependent on DNase I-hypersensitive site 2 (HS2), which contains MARE. The MARE binding activity of Bach1 in K562 and MEL cells increased upon SA treatment, and the increase was diminished by the treatment with hemin. Transient expression of Bach1 suppressed the microLCR activity, and this repressor activity was cancelled by treatment with hemin. The expression of a mutated Bach1 lacking heme-binding sites led to a loss in the heme responsiveness of the microLCR. Furthermore, chromatin immunoprecipitation experiments revealed that Bach1 bound to the MARE of HS2 increased by the treatment of MEL cells with SA, and this was cancelled by hemin. We propose that heme positively regulates the beta-globin gene expression by blocking the interaction of Bach1 with the MARE in the LCR.

Animals↗

PubMed2002

A new ferrochelatase mutation combined with low expression alleles in a Japanese patient with erythropoietic protoporphyria.

We investigated the molecular defect of the ferrochelatase gene in a Japanese patient with erythropoietic protoporphyria (EPP), and identified a novel 16 base pair (574-589) deletion within exon 5. This deletion resulted in a frame-shift mutation and created a premature stop codon at amino acid position 198. The same molecular defect was also identified in his mother and a brother who had symptomatic EPP, but not in his father who was asymptomatic. The subjects with EPP were homozygous for the low expression haplotype, while his father was heterozygous for this haplotype. These results indicate that the combination of a 16 base pair deletion and low expression of the wild-type allelic variant is responsible for EPP in this pedigree.

Adult↗