Satoshi Asada

MURC, a muscle-restricted coiled-coil protein, is involved in the regulation of skeletal myogenesis

Skeletal myogenesis is a multistep process by which multinucleated mature muscle fibers are formed from undifferentiated, mononucleated myoblasts. However, the molecular mechanisms of skeletal myogenesis have not been fully elucidated. Here, we identified muscle-restricted coiled-coil (MURC) protein as a positive regulator of myogenesis. In skeletal muscle, MURC was localized to the cytoplasm with accumulation in the Z-disc of the sarcomere. In C2C12 myoblasts, MURC expression occurred coincidentally with myogenin expression and preceded sarcomeric myosin expression during differentiation into myotubes. RNA interference (RNAi)-mediated knockdown of MURC impaired differentiation in C2C12 myoblasts, which was accompanied by impaired myogenin expression and ERK activation. Overexpression of MURC in C2C12 myoblasts resulted in the promotion of differentiation with enhanced myogenin expression and ERK activation during differentiation. During injury-induced muscle regeneration, MURC expression increased, and a higher abundance of MURC was observed in immature myofibers compared with mature myofibers. In addition, ERK was activated in regenerating tissue, and ERK activation was detected in MURC-expressing immature myofibers. These findings suggest that MURC is involved in the skeletal myogenesis that results from modulation of myogenin expression and ERK activation. MURC may play pivotal roles in the molecular mechanisms of skeletal myogenic differentiation.

Downregulation of Dicer expression by serum withdrawal sensitizes human endothelial cells to apoptosis

Although the modulated expression of Dicer is documented upon neoplastic transformation, little is known of the regulation of Dicer expression by environmental stimuli and its roles in the regulation of cellular functions in primary cells. In this study, we found that Dicer expression was downregulated upon serum withdrawal in human umbilical vein endothelial cells (HUVECs). Serum withdrawal induced a time-dependent repression of Dicer expression, which was specifically rescued by vascular endothelial cell growth factor or sphingosine-1-phosphate. When Dicer expression was silenced by short-hairpin RNA against Dicer, the cells were more prone to apoptosis under serum withdrawal, whereas the rate of apoptosis was comparable with control cells in the serum-containing condition. Real-time PCR-based gene expression profiling identified several genes, the expression of which was modulated by Dicer silencing, including adhesion and matrix-related molecules, caspase-3, and nitric oxide synthase 3 (NOS3). Dicer silencing markedly impaired migratory functions without affecting cell adhesion and repressed phosphorylation of focal adhesion kinase and proline-rich tyrosine kinase 2 in adherent HUVECs. Dicer knockdown upregulated caspase-3 and downregulated NOS3 expression, and serum withdrawal indeed increased caspase-3 and decreased NOS3 expression. Furthermore, the overexpression of Dicer in HUVECs resulted in a marked reduction in apoptosis upon serum withdrawal and a decreased caspase-3 and increased NOS3 expression. The inhibition of NOS activity by Nomega-nitro-L-arginine methyl ester abrogated the effect of Dicer overexpression to rescue the cells from serum withdrawal-induced apoptosis. These results indicated that serum withdrawal decreases Dicer expression, leading to an increased susceptibility to apoptosis through the regulation of caspase-3 and NOS3 expression.

PARM-1 Is an Endoplasmic Reticulum Molecule Involved in Endoplasmic Reticulum Stress-Induced Apoptosis in Rat Cardiac Myocytes

To identify novel transmembrane and secretory molecules expressed in cardiac myocytes, signal sequence trap screening was performed in rat neonatal cardiac myocytes. One of the molecules identified was a transmembrane protein, prostatic androgen repressed message-1 (PARM-1). While PARM-1 has been identified as a gene induced in prostate in response to castration, its function is largely unknown. Our expression analysis revealed that PARM-1 was specifically expressed in hearts and skeletal muscles, and in the heart, cardiac myocytes, but not non-myocytes expressed PARM-1. Immunofluorescent staining showed that PARM-1 was predominantly localized in endoplasmic reticulum (ER). In Dahl salt-sensitive rats, high-salt diet resulted in hypertension, cardiac hypertrophy and subsequent heart failure, and significantly stimulated PARM-1 expression in the hearts, with a concomitant increase in ER stress markers such as GRP78 and CHOP. In cultured cardiac myocytes, PARM-1 expression was stimulated by proinflammatory cytokines, but not by hypertrophic stimuli. A marked increase in PARM-1 expression was observed in response to ER stress inducers such as thapsigargin and tunicamycin, which also induced apoptotic cell death. Silencing PARM-1 expression by siRNAs enhanced apoptotic response in cardiac myocytes to ER stresses. PARM-1 silencing also repressed expression of PERK and ATF6, and augmented expression of CHOP without affecting IRE-1 expression and JNK and Caspase-12 activation. Thus, PARM-1 expression is induced by ER stress, which plays a protective role in cardiac myocytes through regulating PERK, ATF6 and CHOP expression. These results suggested that PARM-1 is a novel ER transmembrane molecule involved in cardiac remodeling in hypertensive heart disease.

Stage-Specific Role of Endogenous Smad2 Activation in Cardiomyogenesis of Embryonic Stem Cells

The role of Smads and their specific ligands during cardiomyogenesis in ES cells was examined. Smad2 was activated bimodally in the early and late phases of cardiac differentiation, whereas Smad1 was activated after the middle phase. Nodal and Cripto were expressed in the early stage and then downregulated, whereas transforming growth factor-β and activin were expressed only in the late phase. Suppression of early Smad2 activation by SB-431542 produced complete inhibition of endodermal and mesodermal induction but augmented neuroectodermal differentiation, followed by poor cardiomyogenesis, whereas inhibition during the late phase alone promoted cardiomyogenesis. Inhibitory effect of Smad2 on cardiomyogenesis in the late phase was mainly mediated by transforming growth factor-β, and inhibition of transforming growth factor-β–mediated Smad2 activation resulted in a greater replicative potential in differentiated cardiac myocytes and enhanced differentiation of nonmyocytes into cardiac myocytes. Thus, endogenous Smad2 activation is indispensable for endodermal and mesodermal induction in the early phase. In the late phase, endogenous transforming growth factor-β negatively regulates cardiomyogenesis through Smad2 activation by modulating proliferation and differentiation of cardiac myocytes.

Hall scattering factors in p-type 4H-SiC with various doping concentrations

The Hall scattering factor (γH) in p-type 4H-SiC with various aluminum doping concentrations of 5.8 × 1014–7.1 × 1018 cm−3 was investigated from 300 to 900 K. γH was determined by comparing the Hall coefficient with the theoretical carrier concentration derived from acceptor and donor concentrations obtained from secondary ion mass spectrometry and capacitance–voltage measurements. γH decreased with increasing temperature or doping concentration; γH = 1–0.4 for the doping concentration of 5.8 × 1014 cm−3 and γH = 0.5–0.2 for the doping concentration of 7.1 × 1018 cm−3. The dependence might be caused by the anisotropic and nonparabolic valence band structure of 4H-SiC.

Design Criterion for SiC BJTs to Avoid ON-Characteristics Degradation Due to Base Spreading Resistance

It is empirically known that the ON-resistance (voltage) of the SiC bipolar junction transistors (BJTs) with a thin-base layer is prone to be larger than the resistance of a voltage-blocking collector layer. In this paper, we explain the mechanism of this degradation of ON-characteristics by focusing on a high base spreading resistance and a parasitic diode existing below the base contact. An equivalent circuit model of the SiC BJT was proposed, and SPICE simulation was performed.In addition, TCAD simulation confirmed the validity of the model well. Based on the model, a design criterion to avoid the unwanted increase of the ON-resistance is proposed.

Temperature dependence of current gain in 4H-SiC bipolar junction transistors

The temperature dependence of current gain from 140 to 460 K in 4H-SiC bipolar junction transistors (SiC BJTs) was investigated. The current gain increased from 110 to 1200 with decreasing temperature from 460 to 200 K. The high current gain at the low temperature can be ascribed to the enhanced incomplete ionization of aluminum acceptors in the base layer, resulting in the increase in injection efficiency. However, when the temperature was further reduced from 200 to 140 K, the current gain decreased from 1200 to 515, which is caused by high injection condition in the base layer, because of a very low hole concentration below 200 K.

Modification of expanded polytetrafluoroethylene valved conduit using the thin-type leaflets

Objectives The expanded polytetrafluoroethylene conduit with fan‐shaped leaflets and bulging sinuses for right ventricular outflow tract reconstruction was modified with a newly developed thin‐type expanded polytetrafluoroethylene leaflet. The purpose of this study was to evaluate the clinical outcomes and hemodynamic performance of the modified conduit. Methods From January 2010 to December 2013, 149 patients underwent definitive right ventricular outflow tract reconstruction using the expanded polytetrafluoroethylene conduit; the 55 patients receiving a conventional conduit (group N) were compared with the 94 patients receiving a modified conduit (group T). Results There were no conduit‐related deaths, operative deaths, or reimplantations for conduit failure. The overall survival and freedom from reintervention for conduit‐related reasons at 3 years were 98.2% versus 95.6% (P = .438) and 94.7% versus 97.9% (P = .954) for groups N and T, respectively. The mean peak pressure gradients were 22.6 ± 15.6 mm Hg versus 18.2 ± 11.5 mm Hg (P = .161), and in the subanalysis within small‐sized conduits, they were 30.2 ± 16.5 mm Hg versus 20.4 ± 10.7 mm Hg (P = .034). Regarding conduit insufficiency, the modified conduit showed a significantly worse grade of insufficiency (P = .014) only in the subanalysis within large‐sized conduits. Conclusions Although the clinical outcomes did not differ within midterm observation, the thin‐type expanded polytetrafluoroethylene leaflet was considered to be suitable for the small‐sized conduits, but not for large‐sized conduits, based on the comparison of the hemodynamic performance. Long‐term follow‐up is necessary to address the appropriate sheet type for middle‐sized conduits and to estimate the durability of the thin‐type leaflet.

Surgical treatment for endocardial radiofrequency ablation-resistant sustained monomorphic ventricular tachycardia with mural thrombus including dense calcification in the left ventricle

Catheter ablation provides effective results for sustained monomorphic ventricular tachycardia (VT), but the presence of mural thrombus including dense calcification occasionally causes unfavorable outcomes. The case of a 67-year-old man in whom sustained monomorphic VT, which was resistant to endocardial radiofrequency ablation, in the presence of mural thrombus including dense calcification after coronary artery bypass grafting was successfully treated by left ventricular reconstruction with cryoablation is reported.

Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC

Previous work has shown that the concentration of shallow dopants in a semiconductor can be estimated from the photoluminescence (PL) spectrum by comparing the intensity of the bound-to-the-dopant exciton emission to that of the free exciton. In this work, we study the low-temperature PL of high-quality uncompensated Al-doped p-type 4H-SiC and propose algorithms for determining the Al-doping concentration using the ratio of the Al-bound to free-exciton emission. We use three different cryogenic temperatures (2, 41, and 79 K) in order to cover the Al-doping range from mid 1014 cm−3 up to 1018 cm−3. The Al-bound exciton no-phonon lines and the strongest free-exciton replica are used as a measure of the bound- and free-exciton emissions at a given temperature, and clear linear relationships are obtained between their ratio and the Al-concentration at 2, 41, and 79 K. Since nitrogen is a common unintentional donor dopant in SiC, we also discuss the criteria allowing one to determine from the PL spectra whethe...