Biomedical subjects

Hajime Honda

Publications and source records attributed to Hajime Honda.

At least 19 recordsLinked to original sources

PubMed2006

Tropomyosin as a regulator of the sliding movement of actin filaments.

We examined the capacity of tropomyosin molecules regulating the sliding movement of actin filaments on myosin molecules in the presence of ATP molecules to be hydrolyzed. For this objective, we prepared tropomyosin molecules modified to be a little bit stiffer compared to the intact ones by applying a fixed cross-linker between a pair of twisted tropomyosin monomers. The cross-linked tropomyosin molecules, when complexed with actin filaments, were found to inhibit the sliding movement of the filaments on myosin molecules even in the absence of calcium-regulated troponin molecules. It is then suggested that the mechanical flexibility of tropomyosin molecules may be instrumental to actualizing the proper functional regulation of the sliding movement of actin filaments.

Actin Cytoskeleton↗

PubMed2006

Unidirectional movement of an actin filament taking advantage of temperature gradients.

An actin filament with heat acceptors attached to its Cys374 residue in each actin monomer could move unidirectionally even under heat pulsation alone, while in the total absence of both ATP and myosin. The prime driver for the movement was temperature gradients operating between locally heated portions on an actin filament and its cooler surroundings. In this report, we investigated how the mitigation of the temperature gradients induces a unidirectional movement of an actin filament. We then observed the transversal fluctuations of the filament in response to heat pulsation and their transition into longitudinally unidirectional movement. The transition was significantly accelerated when Cys374 and Lys336 were simultaneously excited within an actin monomer. These results suggest that the mitigation of the temperature gradients within each actin monomer first went through the energy transformation to transversal fluctuations of the filament, and then followed by the transformation further down to longitudinal movements of the filament. The faster mitigation of temperature gradients within actin monomer helps build up the transition from the transversal to longitudinal movements of the filament by coordinating the interaction between the neighboring monomers.

Actins↗

PubMed2006

Troponin is a potential regulator for actomyosin interactions.

Troponin extracted from rabbit skeletal muscle directly binds to an actin filament in a molar ratio of 1:1 even in the absence of tropomyosin. An actin filament decorated with troponin did not exhibit significant difference from pure actin filaments in the maximum rate of actomyosin ATP hydrolysis and the sliding velocity of the filament examined by means of an in vitro motility assay. However, the relative number of troponin-bound actin filaments moving in the absence of calcium ions decreased to half that in their presence. The amount of HMM bound to the filaments was less than 4% of actin monomers in the presence of TNs. In addition, actin filaments could not move when Tn molecules were bound in the molar ratio of about 1:1 although they sufficiently bind to myosin heads. These results indicate that troponin can transform an actin monomer within a filament into an Off-state without sterically blocking of the myosin-binding sites with tropomyosin molecules.

Actins↗

PubMed2005

The role of leptin in progression of non-alcoholic fatty liver disease.

Since non-alchoholic steatohepatitis (NASH) is often accompanied with metabolic syndrome comprising obesity, type-2 diabetes and hypertension, it is hypothesized that adipocytokines, insulin resistance and autonomic nervous system play crucial roles in disease progression of NASH. On the other hand, hepatic stellate cells (HSCs) have been shown to produce leptin when they get activated during hepatic fibrogenesis. Therefore, we investigated the role of leptin in fibrogenesis in the liver. Xenobiotics-induced liver fibrosis was extremely diminished in ob/ob mice and Zucker (fa/fa) rats, an inborn leptin- and leptin receptor (Ob-R)-deficient animal, respectively. Further, leptin increased transforming growth factor (TGF)-beta mRNA in isolated sinusoidal endothelial cells and Kupffer cells, suggesting that leptin promotes hepatic fibrogenesis through up-regulation of TGF-beta in the liver. Moreover, leptin augmented PDGF-dependent proliferation of HSCs by enhancing downstream intracellular signaling pathways via mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3 kinase (PI3K)/Akt. Taken together, it is postulated that leptin acts as a profibrogenic cytokine in sinusoidal microenvironment. These findings indicate that leptin is one of the key regulators for inflammation and progression of fibrosis in various chronic liver diseases including NASH.

Journal Article↗

PubMed2005

Fourier's law of heat transfer and its implication to cell motility.

Fourier's law of heat transfer addressing temperature differences is intrinsically selective in favoring the mitigation of the differences proceeding as fast as possible. We present an experimental demonstration of such selective behavior of material origin. When an actin filament equipped with nano-scale heat acceptors was placed under heat pulsation, it demonstrated a unidirectional movement without the presence of myosin or ATP. The prime factor for the unidirectional movement was the temperature differences between the locally heated portions on the actin filament and the cooler material bodies in the surroundings. The unidirectional movement could be enhanced in the process of mitigating the temperature differences as fast as possible.

Actin Cytoskeleton↗

PubMed2005

Enantiomeric excess of amino acids in hydrothermal environments.

In a simulated hydrothermal environment allowing fluid circulation between hot and cold regions repeatedly, D- and L-alanine molecules were racemized differently depending upon the concentration of alanine, whether D or L, present in the solution. In particular, the relative population of L-alanine was slightly more enhanced compared to that of D-alanine when the concentration of alanine increased. Enantiomeric excess of L-alanine was also observed when metallic ions such as zinc were sufficiently present in the environments. Hydrothermal environments in the primitive ocean could have maintained the capacity of selectively retaining enantiomeric excess in favor of L-amino acids once the concentration of amino acids could reach a sufficiently high level.

Alanine↗

PubMed2005

Evolving lipid vesicles in prebiotic hydrothermal environments.

We compared three different kinds of lipid vesicles made of saturated fatty acids, unsaturated fatty acids, and phospholipids for their evolutionary capabilities in a simulated hydrothermal environment. Encapsulation of the glycine monomers enhanced the oligomerization of peptides in all cases. Fatty acid vesicles remained stable at higher temperatures and efficiently utilized heat energy for this synthetic reaction. Phospholipid vesicles were destabilized by higher temperatures, and thus were found to be better suited to enhance synthetic reactions at lower temperatures.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Enhancing the staggered fluctuations of an actin filament sliding on Chara myosin.

We examined both longitudinal and transversal fluctuations of displacements of an actin filament sliding upon Chara myosin molecules. Although the magnitude of transversal fluctuations remained rather independent of ATP concentration, the longitudinal ones were found to increase their magnitude as the concentration increased. In addition, the longitudinal fluctuations gradually increased as the sliding velocity of the filament increased.

Actin Cytoskeleton↗

PubMed2004

Transition from contractile to protractile distortions occurring along an actin filament sliding on myosin molecules.

An ATP-activated actin filament sliding on myosin molecules exhibited mechanical distortions or fluctuations both longitudinally and transversally along the filament. Although actin filaments exhibited a uniform sliding movement longitudinally as the ATP concentration increased, the longitudinal fluctuations were found to vary their magnitude with the concentration. The magnitude of longitudinal fluctuations reached its maximum at approximately 100 microM of the ATP concentration. The local enhancement of the longitudinal fluctuations as responding to changes in the ATP concentration is associated with a critical phenomenon bridging the two different kinds of mechanical distortions, either contractile or protractile ones, occurring within a sliding actin filament.

Actins↗

PubMed2004

Expression of leptin receptors in hepatic sinusoidal cells.

Emerging evidence has suggested a critical role of leptin in hepatic inflammation and fibrogenesis, however, the precise mechanisms underlying the profibrogenic action of leptin in the liver has not been well elucidated. Therefore, the present study was designed to investigate the expression and functions of leptin receptors (Ob-R) in hepatic sinusoidal cells. Hepatic stellate cells (HSCs), Kupffer cells and sinusoidal endothelial cells (SECs) were isolated from rat livers by in situ collagenase perfusion followed by differential centrifugation technique, and expression of Ob-Ra and Ob-Rb, short and long Ob-R isoforms, respectively, were analyzed by RT-PCR. Ob-Ra mRNA was detected ubiquitously in HSCs and SECs. In contrast, Ob-Rb was detected clearly only in SECs and Kupffer cells, but not in 7-day cultured HSCs. Indeed, tyrosine-phosphorylation of STAT-3, a downstream event of Ob-Rb signaling, was observed in SECs, but not in HSCs, 1 hr after incubation with leptin. Further, leptin increased AP-1 DNA binding activity and TGF-beta 1 mRNA levels in Kupffer cells and SECs, whereas leptin failed to increase TGF-beta 1 mRNA in HSCs. These findings indicated that SECs and Kupffer cells, but not HSCs, express functional leptin receptors, through which leptin elicits production of TGF-beta 1. It is hypothesized therefore that leptin, produced systemically from adipocytes and locally from HSCs, up-regulates TGF-beta 1 thereby facilitate tissue repairing and fibrogenesis in the sinusoidal microenvironment.

Journal Article↗

PubMed2004

Significance of kinetic degrees of freedom in operation of the actomyosin motor.

The actomyosin motor as a principal functional component of cell motility is highly coordinated in regulating the participating molecular components. At the same time, it has to be flexible and plastic enough to accommodate itself to a wide variety of operational conditions. We prepared two different types of actomyosin systems. One is a natural intact actomyosin system with no artificial constraint on the kinetic degrees of freedom of the actin filaments, and the other is a regulated one with actin filaments supplemented by intra- and intermolecular crosslinking to suppress the kinetic degrees of freedom to a certain extent. Crosslinked actomyosin systems were found to remain almost insensitive to calcium regulation even when intact troponin-tropomyosin regulatory component was incorporated. Both the ATPase and the motile activities of the actin filaments sliding on myosin molecules were markedly lowered by the crosslinking. In contrast, once the crosslinking was cleaved, both properties returned to the normal as with intact actomyosin systems.

Actomyosin↗

PubMed2004

Phosphorylation of nucleotide molecules in hydrothermal environments.

Phosphorylation of AMP into ADP and ATP, that can outrun their hydrolysis, was made possible in a simulated hydrothermal environment when trimetaphosphate was used as the phosphate source. The best yields of phosphorylated products were obtained when the reaction fluids whose temperature was set at about 100 degrees centigrade was injected into the cold environment maintained at 0 degree in a recycling manner. Hydrothermal environments in the primitive ocean could also have served as prebiotic sites for phosphorylation, among others.

Adenine Nucleotides↗

PubMed2003

Enhancement of the sliding velocity of actin filaments in the presence of ATP analogue: AMP-PNP.

The sliding velocity of actin filaments was found to increase in the presence of ATP analogues. At 0.5 mM ATP, the presence of 2.0 mM of AMP-PNP enhanced the filament velocity from 3.2 up to 4.5 microm/s. However, 2 mM ADP decreased the velocity down to 1.1 microm/s. The results suggest that the complex conformations of myosin cross-bridges interacting with an actin filament in the presence of ATP analogues makes the entire filament move faster.

Actin Cytoskeleton↗

PubMed2003

Amplification of diverse catalytic properties of evolving molecules in a simulated hydrothermal environment.

We observed chemical evolution in a mixture of four amino acids, glycine, L-alanine, L-valine and L-aspartic acid, circulated through a flow reactor simulating the thermodynamic conditions of a hydrothermal environment. These monomers form peptides with tertiary structures and potential catalytic functions. The HPLC profile of synthesized oligomers varied with each particular run, but the products were found to separate into distinct clusters when more than one hundred runs were compared statistically. This observation suggests that chemical evolution on the early Earth had stochastic aspects that must be understood in order to develop useful models of prebiotic evolution.

Alanine↗

PubMed2002

Acute ethanol administration down-regulates toll-like receptor-4 in the murine liver.

Acute ethanol administration temporarily decreases the sensitivity to endotoxin (lipopolysaccharide, LPS) in the liver. The purpose of this study was to investigate the changes of toll-like receptor (TLR)-4, a newly identified LPS receptor in macrophages, in the liver following acute ethanol administration. Male C57BL/6N mice were given a bolus intragastric administration of ethanol (5 mg/g BW) through a gastric canula, and liver samples were obtained 2-48 h later. RAW264.7 macrophages were cultured in the presence of ethanol (100 mM) or LPS (10 ng/ml) for up to 4 h. TLR-4 mRNA in the liver and RAW264.7 cells was detected by RNase protection assay. As expected, TLR-4 mRNA was clearly detected in the control liver; however, it was barely detectable in the liver 2-6 h after ethanol administration, followed by the gradual increase to the basal levels 48 h later. Interestingly, LPS (10 ng/ml), but not ethanol (100 mM), decreased TLR-4 mRNA in RAW264.7 macrophages in 4 h. Indeed, gut-sterilization by oral antibiotics pretreatment prevented the decrease in TLR-4 mRNA caused by acute ethanol administration, supporting the hypothesis that gut-derived endotoxin is involved in the mechanism. These findings clearly indicated that acute ethanol administration in vivo down-regulates TLR-4 expression in the liver. This phenomenon most likely explains the mechanism by which acute ethanol blunts the response of Kupffer cells to LPS transiently.

Journal Article↗

PubMed2002

Prebiotic oligomerization on or inside lipid vesicles in hydrothermal environments.

Oligomerization of amino acids proceeded on or inside lipid vesicles as a model of prebiotic cells in a simulated hydrothermal environment. When the suspension of lipid vesicles taking up monomeric glycine underwent a sudden temperature drop by traversing from a hot (180 degrees C) to a cold (0 degree C) region repeatedly while circulating through a closed reaction circuit, oligopeptides up to heptaglycine were formed even in the absence of condensing agents.

Amino Acids↗

PubMed2002

Leptin receptor-mediated signaling regulates hepatic fibrogenesis and remodeling of extracellular matrix in the rat.

BACKGROUND & AIMS: In this study, we investigated the role of leptin and its receptors (Ob-R) in profibrogenic responses in the liver using Zucker (fa/fa) rats, a natural occurring Ob-R-deficient animal. METHODS: Male Zucker (fa/fa) rats and their lean (+/?) littermates were given intraperitoneal injections of thioacetamide (TAA) (200 mg/kg body wt, 3 times/wk) for 4-8 weeks, and progression of hepatic fibrosis was evaluated. In vitro transactivation of hepatic stellate cells (HSCs) isolated from Zucker rats was evaluated by Western blotting and immunocytochemistry for alpha-smooth muscle actin and type I collagen. Further, a long-form Ob-R (Ob-Rb) in sinusoidal endothelial cells (SECs) and Kupffer cells was identified by reverse-transcription polymerase chain reaction. Moreover, transforming growth factor (TGF)-beta1 messenger RNA in LSE cells, a human SEC-derived cell line, was measured by Northern blotting. RESULTS: Although the normal liver does not produce leptin, activated HSCs produced leptin in vivo during fibrogenesis caused by TAA. In Zucker rats, TAA-induced hepatic fibrosis was prevented almost completely, whereas induction of TGF-beta1 and activation of HSCs were abolished. It is less likely, however, that leptin plays an essential role in the activation of HSCs as a strong autocrine regulator, because HSCs isolated from Zucker rats undergo normal transactivation process in vitro. In contrast, SECs and Kupffer cells contain Ob-Rb, through which leptin up-regulates the expression of matrix remodeling genes including TGF-beta1. CONCLUSIONS: Collectively, these findings indicated that leptin and its functional receptors (Ob-Rb) play a pivotal role in profibrogenic responses in the liver.

Animals↗

PubMed2002

Leptin is required for fibrogenic responses induced by thioacetamide in the murine liver.

In this study, we investigated hepatic fibrogenesis caused by long-term thioacetamide (TAA) administration in ob/ob mice, a naturally occurring leptin deficient animal. In the lean littermates, prominent hepatic fibrosis, as well as positive staining for alpha smooth muscle actin (alpha-SMA), was induced by treatment with TAA (200 microg/g, IP, 3 times per week) for 4 to 8 weeks as expected. In sharp contrast, almost no hepatic fibrosis developed in ob/ob mice given the equivalent doses of TAA, where specific staining for alpha-SMA barely was detected. Induction of alpha1(I) procollagen mRNA caused by TAA also was prevented in ob/ob mice almost completely. Further, transforming growth factor beta (TGF-beta) mRNA was increased in the liver after TAA treatment for 4 weeks in lean littermates, which also was prevented in ob/ob mice. Interestingly, fibrotic septa in the hepatic lobules, as well as increases in alpha1(I) procollagen mRNA, was observed in ob/ob mice, when they were injected with recombinant murine leptin (1 microg/g daily) in combination with TAA treatment. Leptin per se did not cause any fibrotic changes in the liver in ob/ob mice. These findings clearly indicated that leptin deficiency is responsible for the resistance to TAA-induced profibrogenic responses in ob/ob mice. In conclusion, leptin appears to promote profibrogenic responses in the liver, in part, by up-regulation of TGF-beta.

Actins↗