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Articles by K Takeuchi
Total Records ( 6 ) for K Takeuchi
  K Takeuchi and K. Reue
 

Triacylglycerol (TAG) synthesis and storage in tissues such as adipose tissue and liver have important roles in metabolic homeostasis. The molecular identification of genes encoding enzymes that catalyze steps in TAG biosynthesis from glycerol 3-phosphate has revealed an unexpected number of protein isoforms of the glycerol phosphate acyltransferase (GPAT), acylglycerolphosphate acyltransferase (AGPAT), and lipin (phosphatidate phosphatase) families that appear to catalyze similar biochemical reactions. However, on the basis of available data for a few members in which genetic deficiencies in mouse and/or human have been studied, we postulate that each GPAT, AGPAT, and lipin family member likely has a specialized role that may be uncovered through careful biochemical and physiological analyses.

  M Asai , K Takeuchi , M Saotome , T Urushida , H Katoh , H Satoh , H Hayashi and H. Watanabe
  Aims

Hypoxia, ischaemia, and exogenous chemicals can induce extracellular and intracellular acidosis, but it is not clear which of these types of acidosis affects endothelial cell function. The synthesis and release of endothelium-derived relaxing factors (EDRFs) are linked to an increase in cytosolic Ca2+ concentration, and we therefore examined the effects of extracellular and intracellular acidosis on Ca2+ responses and EDRF production in cultured porcine aortic endothelial cells.

Methods and results

Cytosolic pH (pHi) and Ca2+ were measured using fluorescent dyes, BCECM/AM (pH-indicator) and fura-2/AM (Ca2+-indicator), respectively. EDRFs, nitric oxide (NO) and prostaglandin I2 (PGI2) were assessed using DAF-FM/DA (NO-indicator dye) fluorometry and 6-keto PGF1 enzyme immunoassay, respectively. HEPES buffers titrated to pH 6.4, 6.9, and 7.4 were used to alter extracellular pH (pHo), and propionate (20 mmol/L) was applied to cause intracellular acidosis. Extracellular acidosis strongly suppressed bradykinin (BK, 10 nmol/L)- and thapsigargin (TG, 1 µmol/L)-induced Ca2+ responses by 30 and 23% at pHo 6.9, and by 80 and 97% at pHo 6.4, respectively. During the examinations, there were no significant differences in pHi among the three groups at pHo 7.4, 6.9, and 6.4. Extracellular acidosis also inhibited BK-stimulated PGI2 production by 55% at pHo 6.9 and by 77% at pHo 6.4, and NO production by 38% at pHo 6.9 and by 91% at pHo 6.4. The suppressive effects of extracellular acidosis on Ca2+ responses and NO production were reversible. Propionate changed pHi from 7.3 to 6.9, without altering pHo (7.4). Intracellular acidosis had no effect on BK- and TG-induced Ca2+ responses or NO production.

Conclusion

These results indicate that extracellular, but not intracellular, acidosis causes endothelial dysfunction by inhibiting store-operated Ca2+ entry, so helping to clarify the vascular pathophysiology of conditions such as ischaemia, hypoxia, acidosis, and ischaemia-reperfusion.

  C Nishiura , K Takeuchi , K Minoura , M Sumida , T Taniguchi , K Tomoo and T. Ishida
 

The inhibition of tau fibrillation is a potential therapeutic target for Alzheimer’s and other neurodegenerative diseases. As a series of studies on inhibiting the transition of soluble monomeric tau into mature fibril, the effect of Tyr310 residue in the third repeat (R3) of the microtubule-binding domain (MBD) on the assembly of MBD was investigated using Tyr-substituted MBD mutants by fluorescence, circular dichroism spectroscopy and electron microscopy. Consequently, the importance of the Tyr residue located at position 310, not at other positions, was clearly shown. The conformational comparison of the Tyr310Ala-substituted R3 repeat peptide with the unsubstituted one showed that the Tyr residue contributes to the rigid extended structure of the N-terminal V306QIVYK311 sequence, and its replacement by Ala leads to the deformation of the extended structure, consequently losing its aggregation ability. The present results indicate that a compound that interacts specifically with the Tyr residue or an antibody recognizing the region containing the Tyr residue becomes a candidate for inhibiting tau fibrillation.

 
 
 
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