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Articles by K Takahashi
Total Records ( 7 ) for K Takahashi
  D Taura , M Sone , K Homma , N Oyamada , K Takahashi , N Tamura , S Yamanaka and K. Nakao
 

Objective— Induced pluripotent stem (iPS) cells are a novel stem cell population derived from human adult somatic cells through reprogramming using a defined set of transcription factors. Our aim was to determine the features of the directed differentiation of human iPS cells into vascular endothelial cells (ECs) and mural cells (MCs), and to compare that process with human embryonic stem (hES) cells.

Methods and Results— We previously established a system for differentiating hES cells into vascular cells. We applied this system to human iPS cells and examined their directed differentiation. After differentiation, TRA1–60 Flk1+ cells emerged and divided into VE-cadherin-positive and -negative populations. The former were also positive for CD34, CD31, and eNOS and were consistent with ECs. The latter differentiated into MCs, which expressed smooth muscle -actin and calponin after further differentiation. The efficiency of the differentiation was comparable to that of human ES cells.

Conclusions— We succeeded in inducing and isolating human vascular cells from iPS cells and indicate that the properties of human iPS cell differentiation into vascular cells are nearly identical to those of hES cells. This work will contribute to our understanding of human vascular differentiation/development and to the development of vascular regenerative medicine.

  S Koganemaru , T Mima , M. N Thabit , T Ikkaku , K Shimada , M Kanematsu , K Takahashi , G Fawi , R Takahashi , H Fukuyama and K. Domen
 

Patients with chronic stroke often show increased flexor hypertonia in their affected upper limbs. Although an intervention strategy targeting the extensors of the affected upper limb might thus be expected to have benefits for functional recovery, conventional repetitive motor training has limited clinical utility. Recent studies have shown that repetitive transcranial magnetic stimulation could induce motor recovery. The present study tested whether 5 Hz repetitive transcranial magnetic stimulation of the upper-limb area of the primary motor cortex, combined with extensor motor training, had a greater effect on motor recovery than either intervention alone in stroke hemiparesis. Nine patients with chronic subcortical stroke and nine age-matched healthy subjects completed the crossover study. In separate sessions, we examined the single intervention effect of repetitive wrist and finger extension exercises aided by neuromuscular stimulation, the single intervention effect of 5 Hz repetitive transcranial magnetic stimulation and the combined effect of the two interventions. The motor functions were evaluated behaviourally in patients (Experiment 1) and electrophysiologically in healthy subjects (Experiment 2), both before and after the intervention. In addition, we tested the long-term effect by repeating the combined interventions 12 times in patients (Experiment 3). The motor functions were measured again 2 weeks after the end of the repetitive intervention period. In Experiment 1, the combined intervention, but neither of the single interventions, resulted in an improvement of extensor movement (P < 0.0001) and grip power (P < 0.05), along with a reduction of flexor hypertonia (P < 0.01), in their paretic upper limbs. In Experiment 2, only the combined intervention resulted in selective plastic changes of cortico-spinal excitability (P < 0.01), motor threshold (P < 0.001) and silent period (P < 0.01) for the extensors. In Experiment 3, we also confirmed long-term beneficial effects of the combined intervention in patients. These findings indicate that combining motor training with repetitive transcranial magnetic stimulation can facilitate use-dependent plasticity and achieve functional recovery of motor impairments that cannot be attained by either intervention alone. This method could be a powerful rehabilitative approach for patients with hemiparetic stroke.

  K Takahashi , A Inage , I.M Rebeyka , D.B Ross , R.B Thompson , A.S Mackie and J.F. Smallhorn
 

Background— Tricuspid regurgitation in hypoplastic left heart syndrome has an impact on outcome, but its mechanisms remain unclear.

Methods and Results— Real-time 3-dimensional echocardiography was performed in 35 patients with hypoplastic left heart syndrome (age, 1 month to 10 years; 10 after first-stage Norwood, 12 after superior cavopulmonary shunt, 13 after Fontan). From the 3-dimensional data set, we marked the annulus in systole and diastole. At mid systole, we marked the location of the papillary muscle tip and point of chordal attachment to the leaflet. We traced the surfaces of the tricuspid valve leaflets and measured the volume of leaflet prolapse, tethering, annular and septal leaflet areas, and papillary muscle position. Seventeen patients had moderate tricuspid regurgitation (prolapse, 7; tethered leaflets, 7) and 18 mild (prolapse, 0; tethered leaflets, 7). Multiple linear regression analysis revealed that moderate tricuspid regurgitation is associated with leaflet tethering and prolapse; that in hypoplastic left heart syndrome with tethered leaflets, the papillary muscle is displaced laterally and the tricuspid annulus is more planar; and that enlargement of the annulus at mid systole, small septal leaflet area, and age affect the degree of prolapse.

Conclusion— In hypoplastic left heart syndrome, moderate tricuspid regurgitation may be associated with increasing age, geometrical changes of the annulus, leaflet prolapse, lateral papillary muscle displacement, and subsequent leaflet tethering, as well as a smaller septal leaflet.

  F Savarese , A Davila , R Nechanitzky , I De La Rosa Velazquez , C. F Pereira , R Engelke , K Takahashi , T Jenuwein , T Kohwi Shigematsu , A. G Fisher and R. Grosschedl
 

Satb1 and the closely related Satb2 proteins regulate gene expression and higher-order chromatin structure of multigene clusters in vivo. In examining the role of Satb proteins in murine embryonic stem (ES) cells, we find that Satb1–/– cells display an impaired differentiation potential and augmented expression of the pluripotency determinants Nanog, Klf4, and Tbx3. Metastable states of self-renewal and differentiation competence have been attributed to heterogeneity of ES cells in the expression of Nanog. Satb1–/– cultures have a higher proportion of Nanoghigh cells, and an increased potential to reprogram human B lymphocytes in cell fusion experiments. Moreover, Satb1-deficient ES cells show an increased expression of Satb2, and we find that forced Satb2 expression in wild-type ES cells antagonizes differentiation-associated silencing of Nanog and enhances the induction of NANOG in cell fusions with human B lymphocytes. An antagonistic function of Satb1 and Satb2 is also supported by the almost normal differentiation potential of Satb1–/–Satb2–/– ES cells. Taken together with the finding that both Satb1 and Satb2 bind the Nanog locus in vivo, our data suggest that the balance of Satb1 and Satb2 contributes to the plasticity of Nanog expression and ES cell pluripotency.

  D Shindo , K Takahashi , Y Murakami , K Yamazaki , S Deguchi , H Suga and Y. Kondo
 

The double-probe piezodriving specimen holder that was recently developed by some of the present authors is modified to introduce a laser irradiation port in one of its two arms. As a result, the new specimen holder consists of a piezodriving probe and a laser irradiation port, both of which can be three-dimensionally controlled by using piezoelectric elements and micrometers. While the piezodriving probe interacts with the specimen set in the holder in several ways, the laser beam causes photo-induced phenomena to occur. By performing electron holography using the new specimen holder, we demonstrate that it is possible to evaluate the change in the electric field resulting from the discharging effect of laser irradiation on organic photoconductors.

  K Nagao , Y Zhao , K Takahashi , Y Kimura and K. Ueda
 

ABCA1 plays a major role in HDL metabolism. Cholesterol secretion by ABCA1 is dependent on the presence of extracellular acceptors, such as lipid-free apolipoprotein A-I (apoA-I). However, the importance of the direct interaction between apoA-I and ABCA1 in HDL formation remains unclear. In contrast, ABCB4 mediates the secretion of phospholipids and cholesterol in the presence of sodium taurocholate (NaTC) but not in the presence of apoA-I. In this study, we analyzed apoA-I binding and NaTC-dependent lipid efflux by ABCA1. ABCA1 mediated the efflux of cholesterol and phospholipids in the presence of NaTC as well as in the presence of apoA-I in an ATP-dependent manner. The Tangier disease mutation W590S, which resides in the extracellular domain and impairs apoA-I-dependent lipid efflux, greatly decreased NaTC-dependent cholesterol and phospholipid efflux. However, the W590S mutation did not impair apoA-I binding and, conversely, retarded the dissociation of apoA-I from ABCA1. These results suggest that the W590S mutation impairs ATP-dependent lipid translocation and that lipid translocation or possibly lipid loading, facilitates apoA-I dissociation from ABCA1. NaTC is a good tool for analyzing ABCA1-mediated lipid efflux and allows dissection of the steps of HDL formation by ABCA1.

  T Kanzaki , S Ushioku , A Nakagawa , T Oka , K Takahashi , T Nakamura , K Kuwajima , A Yamagishi and M. Yohda
 

Group II chaperonins exist in archaea and the eukaryotic cytosol, and mediate protein folding in an ATP-dependent manner. We have been studying the reaction mechanism of group II chaperonins using chaperonin, the recombinant chaperonin subunit homo-oligomer from a hyperthermophilic archaeon, Thermococcus sp. strain KS-1 (T. KS-1). Although the high stability and activity of T. KS-1 chaperonin provided advantages for our study, its high thermophilicity caused the difficulty in using various analytical methods. To resolve this problem, we tried to adapt T. KS-1 chaperonin to moderate temperatures by mutations. The comparison of amino acid sequences between 26 thermophilic and 17 mesophilic chaperonins showed that three amino acid replacements are likely responsible for the difference of their optimal temperatures. We introduced three single mutations and also their double combinations into T. KS-1 chaperonin. Among them, K323R single mutant exhibited the improvements of the folding activity and the ATP-dependent conformational change ability at lower temperatures, such as 50°C and 40°C. Since K323 may secure helix 12 in the closed conformation by interacting with D198, the replacement of Lys to Arg likely induced the higher mobility of the built-in lid, resulting in the higher activity at relatively low temperatures.

 
 
 
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