Takako T. Ishii

Adipose Tissue–Specific Regulation of Angiotensinogen in Obese Humans and Mice: Impact of Nutritional Status and Adipocyte Hypertrophy

BACKGROUND The adipose tissue renin-angiotensin system (RAS) has been implicated in the pathophysiology of obesity and dysfunction of adipose tissue. However, neither regulation of angiotensinogen (AGT) expression in adipose tissue nor secretion of adipose tissue-derived AGT has been fully elucidated in humans. METHODS Human subcutaneous abdominal adipose tissue (SAT) biopsies were performed for 46 subjects with a wide range of body mass index (BMI). Considering the mRNA level of AGT and indices of body fat mass, the amount of adipose tissue-derived AGT secretion (A-AGT-S) was estimated. Using a mouse model of obesity and weight reduction, plasma AGT levels were measured with a newly developed enzyme-linked immunosorbent assay (ELISA), and the contribution of A-AGT-S to plasma AGT levels was assessed. RESULTS A-AGT-S was substantially increased in obese humans and the value was correlated with the plasma AGT level in mice. A-AGT-S and plasma AGT were higher in obese mice, whereas lower in mice with weight reduction. However, the AGT mRNA levels in the liver, kidney, and aorta were not altered in the mouse models. In both humans and mice, the AGT mRNA levels in mature adipocytes (MAs) were comparable to those in stromal-vascular cells. Coulter Multisizer analyses revealed that AGT mRNA levels in the MAs were inversely correlated with the average size of mature adipocytes. CONCLUSIONS This study demonstrates that adipose tissue-derived AGT is substantially augmented in obese humans, which may contribute considerably to elevated levels of circulating AGT. Adipose tissue-specific regulation of AGT provides a novel insight into the clinical implications of adipose tissue RAS in human obesity.

Genetic and Pharmacological Inhibition of Rho-associated Kinase II Enhances Adipogenesis

Rho-associated kinase (ROCK) regulates reorganization of actin cytoskeleton. During adipogenesis, the structure of filamentous actin is converted from long stress fibers to cortical actin, suggesting that the ROCK is involved in adipogenesis. Two ROCK isoforms have been identified: ROCK-I and ROCK-II. However, pharmacological inhibitors of ROCK cannot distinguish two ROCK isoforms. In the present study, we examined the role of ROCK in adipogenesis and actin cytoskeleton using genetic and pharmacological approaches. Y-27632, which inhibits the activity of both ROCK isoforms, enhanced adipogenesis through the up-regulation of adipogenic transcription factors in 3T3-L1 cells. Furthermore, Y-27632 restored inhibition of adipogenesis by lysophosphatidic acid, which activates Rho. Regarding actin cytoskeleton, Y-27632 disrupted stress fibers in 3T3-L1 preadipocytes. Next, we analyzed adipogenesis of mouse embryonic fibroblasts (MEFs) derived from ROCK-I and ROCK-II knock-out mice, respectively. Adipogenesis of ROCK-II (-/-) MEFs was markedly enhanced compared with wild-type MEFs while that of ROCK-I (-/-) MEFs was not. In contrast to pharmacological approaches, no obvious alteration was found in actin cytoskeleton of ROCK-II (-/-) MEFs compared with wild-type MEFs. In 3T3-L1 cells, knockdown of ROCK-II by RNA interference enhanced the expression of adipogenic transcription factors while that of ROCK-I did not. Moreover, Y-27632 inhibited IRS-1 serine phosphorylation and enhanced Akt phosphorylation in 3T3-L1 preadipocytes. Similarly, Akt phosphorylation in ROCK-II (-/-) MEFs was augmented compared with wild-type MEFs. In conclusion, inhibition of ROCK-II, not ROCK-I, enhances adipogenesis accompanied by the up-regulation of adipogenic transcription factors. Augmentation of insulin signaling may contribute to the enhancement of adipogenesis.

The Luminosity Function of IRAS Point Source Catalog Redshift Survey Galaxies

We estimated the luminosity function (LF) of IRAS galaxies in the Point Source Catalog Redshift (PSCz) survey. The faint end of the PSCz LF is slightly steeper than that of the LF derived by Saunders et al. Using an analytical form for the LF used by Saunders et al., we obtain the following parameters: α = 1.23 ± 0.04, L* = (8.85 ± 1.75) × 108 h-2 L☉, σ = 0.724 ± 0.010, and * = (2.34 ± 0.30) × 10-2 h3 Mpc-3. We also examined the evolution in the sample by the simple assumption *(z) ∝ (1 + z)P and found P = 3.40 ± 0.70. It does not affect the three parameters α, L*, and σ, but *(z = 0) is overestimated by up to ~15% if we ignore evolution. We estimated the temperature dependence of the LF. The LFs of warm and cool galaxies are quite different: the LF of warm galaxies has a very steep faint end with α = 1.37. We also discuss a lump found at the brightest end of the LF.We estimated the luminosity function (LF) of IRAS galaxies in the PSCz catalogue. The faint end of the PSCz LF is slightly steeper than that of the LF derived by Saunders et al. (1990; S90). Using an analytical form for the LF used by S90, we obtain the following parameters: α = 1.23± 0.04, L∗ = (8.85± 1.75)× 108h−2 L⊙, σ = 0.724± 0.010, and φ∗ = (2.34± 0.30)× 10−2h3 Mpc−3. We also examined the evolution in the sample by a simple assumption φ∗(z) ∝ (1 + z)P, and found P = 3.40±0.70. It does not affect the three parameters, α, L∗, and σ, but φ∗(z = 0) is overestimated up to ∼ 15 % if we ignore evolution. We estimated the temperature dependence of the LF. The LFs of warm and cool galaxies are quite different: the LF of warm galaxies has a very steep faint end with α = 1.37. We also discuss a lump found at the brightest end of the LF. Subject headings: galaxies: luminosity function, mass function — galaxies: statistics — infrared: galaxies — methods: statistical

Evolution of Conjugate Footpoints inside Flare Ribbons during a Great Two-Ribbon Flare on 2001 April 10

We report a detailed examination of the fine structure inside flare ribbons and the temporal evolution of such structure during an X2.3 solar flare, which occurred on 2001 April 10. We examined fine structures, such as systems of conjugate footpoints, inside flare ribbons by using the Hα images obtained with the Sartorius telescope at Kwasan Observatory, Kyoto University. We identified the conjugate footpoints of each Hα kernel in both flare ribbons by a new method that uses cross-correlation functions of the light curves. We also compared the sites of the Hα kernels with the spatial configurations of flare loops seen in the extreme-ultraviolet images obtained with the Transition Region and Coronal Explorer. We found that the highly correlated pairs of Hα kernels were connected by flare loops seen in the 171 A images. Investigating such fine structures inside the flare ribbons, we can follow the history of energy release and perhaps acquire key information about particle acceleration.

Can Superflares Occur on Our Sun

Recent observations of solar type stars with the Kepler satellite by Maehara et al. have revealed the existence of superflares (with energy of 10^33 - 10^35 erg) on Sun-like stars, which are similar to our Sun in their surface temperature (5600 K - 6000 K) and slow rotation (rotational period > 10 days). From the statistical analysis of these superflares, it was found that superflares with energy 10^34 erg occur once in 800 years and superflares with 10^35 erg occur once in 5000 years on Sun-like stars. In this paper, we examine whether superflares with energy of 10^33 - 10^35 erg could occur on the present Sun through the use of simple order-of-magnitude estimates based on current ideas relating to the mechanisms of the solar dynamo.

EMERGENCE OF A TWISTED MAGNETIC FLUX BUNDLE AS A SOURCE OF STRONG FLARE ACTIVITY

Sunspot proper motions and flares of a super active region NOAA 5395—the largest and most flare-active region in the 22d sunspot cycle—were analyzed in detail. We measured sunspot proper motions by using the Hα - 5.0 A images obtained with the 60 cm Domeless Solar Telescope (DST) at Hida Observatory, Kyoto University and found some peculiar vortex-like motions of small satellite spots, which successively emerged from the leading edge of this sunspot group. To explain these motions of small sunspots, we proposed a schematic model of the successive emergence of twisted and winding magnetic flux loops coiling around a trunk of a magnetic flux tube. The location of the strongest flare activity was found to coincide with the site of the vortex-like motions of sunspots. We conclude that the flare-productive magnetic shear is produced by the emergence of the twisted magnetic flux bundle. Magnetic energy is stored in the twisted flux bundle, which is originally formed in the convection zone and released as flares in the course of the emergence of the twisted flux bundle above the photosphere.

Superflares on Solar-type Stars Observed with Kepler II. Photometric Variability of Superflare-generating Stars: A Signature of Stellar Rotation and Starspots

We performed simple spot-model calculations for quasi-periodic brightness variations of solar-type stars showing superflares using Kepler photometric data. Most of the superflare stars show quasi-periodic brightness modulations with a typical period of one to a few tens of days. Our results indicate that these brightness variations can be explained by the rotation of a star with fairly large starspots. Using the results of the period analysis, we investigated the relation between the energy and frequency of superflares and the rotation period. Stars with relatively slower rotation rates can still produce flares that are as energetic as those of more rapidly rotating stars although the average flare frequency is lower for more slowly rotating stars. We found that the energy of superflares is related to the total coverage of the starspot. The correlation between the spot coverage and the flare energy in superflares is similar to that in solar flares. These results suggest that the energy of superflares can be explained by the magnetic energy stored around the starspots.

Tests of Statistical Methods for Estimating Galaxy Luminosity Function and Applications to the Hubble Deep Field

We study statistical methods for the estimation of the luminosity function (LF) of galaxies. We focus on four nonparametric estimators: the 1/Vmax estimator, the stepwise maximum-likelihood estimator, Choloniewskis estimator, and the improved Lynden-Bell estimator. The performance of the 1/Vmax estimator has recently been questioned, especially for the faint-end estimation of the LF. We improve these estimators for studies of the distant universe, and examine their performances for various classes of functional forms by Monte Carlo simulations. We also apply these estimation methods to the mock Two-Degree Field (2dF) redshift survey catalog prepared by Cole et al. We find that the 1/Vmax estimator yields a completely unbiased result if there is no inhomogeneity, but is not robust against clusters or voids. This is consistent with the well-known results, and we do not confirm the bias trend of 1/Vmax claimed by Willmer in the case of a homogeneous sample. We also find that the other three maximum-likelihood type estimators are quite robust and give consistent results with each other. In practice, we recommend Choloniewskis estimator for two reasons: (1) it simultaneously provides the shape and normalization of the LF; and (2) it is the fastest among these four estimators, because of its algorithmic simplicity. We then analyze the photometric redshift data of the Hubble Deep Field prepared by Fernandez-Soto et al. using the above four methods. We also derive the luminosity density, ρL, at the B and I bands. Our B-band estimation is roughly consistent with that of Sawicki, Lin, & Yee, but it is a few times lower at 2.0 < z < 3.0. The evolution of ρL(I) is found to be less prominent.

PLASMA EJECTIONS FROM A LIGHT BRIDGE IN A SUNSPOT UMBRA

We present conspicuous activities of plasma ejections along a light bridge of a stable and mature sunspot in NOAA Active Region 8971 on 2000 May 2. We found the ejections both in the Hα (104 K) images obtained with the Domeless Solar Telescope at Hida Observatory and in the 171 A (Fe IX/Fe X; ~106 K) images obtained with the Transition Region and Coronal Explorer. Main characteristics of the ejections are as follows: (1) Ejections occur intermittently and recurrently. (2) The velocities and the timings of the 171 A ejections are the same as those of Hα ejections. (3) The appearance of the ejections are different from one another; i.e., the Hα ejections have a jetlike appearance, while the 171 A ejections are like loops.

Spectropolarimetric Observation of an Emerging Flux Region: Triggering Mechanisms of Ellerman Bombs

A high spatial resolution observation of an emerging flux region (EFR) was made using a vector magnetograph and a Hα Lyot filtergraph with the Domeless Solar Telescope at Hida Observatory on 2006 October 22. In Hα wing images, we could see many Ellerman bombs (EBs) in the EFR. Observations in two modes, slit scan and slit fixed, were performed with the vector magnetograph, along with the Hα filtergraph. Using the Hα wing images, we detected 12 EBs during the slit scan observation period and 9 EBs during the slit fixed observation period. With the slit scan observation, we found that all the EBs were distributed in the area where the spatial gradient of vertical field intensity was large, which indicates the possibility of rapid topological change in the magnetic field in the area of EBs. With the slit fixed observation, we found that EBs were distributed in the areas of undulatory magnetic fields, in both the vertical and horizontal components. This paper is the first to report the undulatory pattern in the horizontal components of the magnetic field, which is also evidence for emerging magnetic flux triggered by the Parker instability. These results allow us to confirm the association between EBs and emerging flux tubes. Three triggering mechanisms for EBs are discussed with respect to emerging flux tubes: 9 out of 21 EBs occurred at the footpoints of emerging flux tubes, 8 occurred at the top of emerging flux tubes, and 4 occurred in the unipolar region. Each case can be explained by magnetic reconnection in the low chromosphere.