PubMed Health⌕ Search

Biomedical subjects

Takuji Shirasawa

Publications and source records attributed to Takuji Shirasawa.

At least 19 recordsLinked to original sources
PubMed2007

Polymorphisms in pro- and anti-inflammatory cytokine genes and susceptibility to atherosclerosis: a pathological study of 1503 consecutive autopsy cases.

Atherosclerosis is a chronic inflammatory disease in the intima of the arterial wall, where cytokines play a crucial role in the pathogenesis of this disease. However, the question of whether or not genetic variations in the cytokine genes could influence the development of atherosclerosis has been poorly investigated. We investigated the relationship of nine common single-nucleotide polymorphisms (SNPs) in tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-10, IL-4 and transforming growth factor (TGF)-beta1 with the atherosclerotic severity in 10 different arteries based on 1503 consecutive autopsies of elderly Japanese subjects registered in the Japanese SNPs for geriatric research (JG-SNP) study. The -1031C allele of TNF-alpha was a significant protective factor for atherogenesis in the carotid, femoral and intracranial arteries [odds ratio (OR): 0.72, 0.73 and 0.70, respectively]. The -511T of IL-1beta and the +29T of TGF-beta1 were significant risk factors for atherogenesis in the subclavian and intracranial arteries (OR: 1.35 and 1.48, respectively). In contrast, conventional risk factors for atherogenesis, such as hypertension and diabetes mellitus, conferred independent risks for almost all arteries. Functional SNPs in TNF-alpha, IL-1beta and TGF-beta1 genes play a role in atherogenesis, although their influences are less pronounced than those of conventional risk factors and appear to be limited to specific arteries in the Japanese elderly.

Aged↗
PubMed2006

Accelerated acquisition of permeability barrier function in the skin of presenilin-1-deficient embryos.

Presenilin-1 (PS1) is a transmembrane protein and is responsible for the development of early-onset familial Alzheimer's disease. PS1 is essential for neurogenesis, somitogenesis, angiogenesis and cardiac morphogenesis. We report here that PS1 is involved in the development of skin barrier function. PS1-deficient embryos showed an accelerated acquisition of permeability barrier function at embryonic day 17.5 as manifested by the exclusion of a dye solution. While the expression of beta-catenin and epidermal differentiation markers such as keratin 1 and loricrin was not substantially altered, an increased accumulation of E-cadherin was observed immunohistochemically in the mutant skin. These results suggest that PS1 regulates the acquisition of permeability barrier function in the skin.

Animals↗
PubMed2006

Oxidative stress causes heart failure with impaired mitochondrial respiration.

Elderly people insidiously manifest the symptoms of heart failure, such as dyspnea and/or physical disabilities in an age-dependent manner. Although previous studies suggested that oxidative stress plays a pathological role in the development of heart failure, no direct evidence has been documented so far. In order to investigate the pathological significance of oxidative stress in the heart, we generated heart/muscle-specific manganese superoxide dismutase-deficient mice. The mutant mice developed progressive congestive heart failure with specific molecular defects in mitochondrial respiration. In this paper, we showed for the first time that the oxidative stress caused specific morphological changes of mitochondria, excess formation of superoxide (O(2)(*)(-)), reduction of ATP, and transcriptional alterations of genes associated with heart failure in respect to cardiac contractility. Accordingly, administration of a superoxide dismutase mimetic significantly ameliorated the symptoms. These results implied that O(2)(*)(-) generated in mitochondria played a pivotal role in the development and progression of heart failure. We here present a bona fide model for human cardiac failure with oxidative stress valuable for therapeutic interventions.

Animals↗
PubMed2006

CuZn-SOD deficiency causes ApoB degradation and induces hepatic lipid accumulation by impaired lipoprotein secretion in mice.

Elevated hepatic reactive oxygen species play an important role in pathogenesis of liver diseases, such as alcohol-induced liver injury, hepatitis C virus infection, and nonalcoholic steatohepatitis. In the present study, we investigated and compared the hepatic lipid metabolisms of liver-specific Sod2 (superoxide dismutase 2) knock-out (Sod2 KO), Sod1 knock-out (Sod1 KO), and Sod1/liver-specific Sod2 double knock-out mice (double KO). We observed significant increases in lipid peroxidation and triglyceride (TG) in the liver of Sod1 KO and double KO mice but not in the liver of Sod2 KO mice. We also found that high fat diet enhanced fatty changes of the liver in Sod1 KO and double KO mice but not in Sod2 KO mice. These data indicated that CuZn-SOD deficiency caused lipid accumulation in the liver. To investigate the molecular mechanism of hepatic lipid accumulation in CuZn-SOD-deficient mice, we measured TG secretion rate from liver using Triton WR1339. We found significant decrease of TG secretion in CuZn-SOD-deficient mice. Furthermore, we observed marked degradation of apolipoprotein B (apoB) in the liver and plasma of CuZn-SOD-deficient mice, indicating that degradation of apoB impairs secretion of lipoprotein from the liver. Our data suggest that oxidative stress enhances hepatic lipid accumulation by impaired lipoprotein secretion due to the degradation of apoB in liver.

Animals↗
PubMed2006

Drusen, choroidal neovascularization, and retinal pigment epithelium dysfunction in SOD1-deficient mice: a model of age-related macular degeneration.

Oxidative stress has long been linked to the pathogenesis of neurodegenerative diseases; however, whether it is a cause or merely a consequence of the degenerative process is still unknown. We show that mice deficient in Cu, Zn-superoxide dismutase (SOD1) have features typical of age-related macular degeneration in humans. Investigations of senescent Sod1(-/-) mice of different ages showed that the older animals had drusen, thickened Bruch's membrane, and choroidal neovascularization. The number of drusen increased with age, and exposure of young Sod1(-/-) mice to excess light induced drusen. The retinal pigment epithelial cells of Sod1(-/-) mice showed oxidative damage, and their beta-catenin-mediated cellular integrity was disrupted, suggesting that oxidative stress may affect the junctional proteins necessary for the barrier integrity of the retinal pigment epithelium. These observations strongly suggest that oxidative stress may play a causative role in age-related retinal degeneration, and our findings provide evidence for the free radical theory of aging. In addition, these results demonstrate that the Sod1(-/-) mouse is a valuable animal model to study human age-related macular degeneration.

Animals↗
PubMed2006

Conditional knockout of Mn superoxide dismutase in postnatal motor neurons reveals resistance to mitochondrial generated superoxide radicals.

Mitochondrial dysfunction and oxidative damage are implicated in the pathogenesis of neurodegenerative disease. Mice deficient in the mitochondrial form of superoxide dismutase (SOD2) die during embryonic or early postnatal development, precluding analysis of a pathological role for superoxide in adult tissue. Here, we generated postnatal motor neuron-specific SOD2 knockouts by crossing mice with floxed SOD2 alleles to VAChT-Cre transgenic mice in which Cre expression is restricted to postnatal somatomotor neurons. SOD2 immunoreactivity was specifically lost in a subset of somatomotor neurons resulting in enhanced superoxide production. Yet extensive histological examination revealed no signs of oxidative damage in animals up to 1 year after birth. However, disorganization of distal nerve axons following injury was accelerated in SOD2-deficient motor neurons. These data demonstrate that postnatal motor neurons are surprisingly resistant to oxidative damage from mitochondrial-derived superoxide radicals, but that such damage may sensitize axons to disorganization following nerve injury.

Animals↗
PubMed2006

Standard organ weights among elderly Japanese who died in hospital, including 50 centenarians.

The present study was conducted to determine standard organ weights among the elderly, because little has been reported on this subject. To analyze the human aging process in terms of organ weights, age-associated changes and correlations among organ weights and the contributions of age and nutrition to organ weights were also examined. The subjects included 1615 consecutive autopsy cases of patients aged 60-99 years who died between 1995 and 2003, and cases of 50 centenarians who died between 1973 and 2005. The weights of nine organs were measured before formalin fixation. If affected by serious diseases, such as cancer, the organs were excluded from the study. Values beyond 99% of the bilateral measurement limits were also excluded. In this manner the standard organ weights were obtained. The organ weights decreased significantly according to age in all organs except for the heart in men and the lungs in both genders. Undernutrition strongly contributed to organ weight except for the hypophysis, and was especially apparent in the heart and liver. In conclusion, the standard organ weights of elderly patients who died while hospitalized were determined. Undernutrition contributed significantly to a reduction in organ weights.

Aged↗
PubMed2005

Presenilin-1 controls the growth and differentiation of endothelial progenitor cells through its beta-catenin-binding region.

Presenilin-1 (PS1) is a gene responsible for the development of early-onset familial Alzheimer's disease. Targeted disruption of the PS1 gene in mice suggested that PS1 might be involved in angiogenesis. We have used an in vitro embryonic stem (ES) cell culture system to prepare endothelial progenitor cells (EPC) lacking PS1 and investigated the roles of PS1 in endothelial cell lineage. With this system, Flk-1+ E-cadherin- EPC were generated from PS1-deficient ES cells, and the EPC lacking PS1 as well as wild-type EPC grew to form VE-cadherin+ endothelial colonies supported by a layer of OP9 stromal cells. Although the endothelial colonies from PS1-deficient EPC showed morphology similar to those from wild-type EPC, the PS1-deficient EPC formed a large number of the colonies compared to wild-type EPC. The enhanced colony-forming ability of PS1-deficient EPC was attenuated by the inductions of wild-type human PS1. To differentiate multiple activities of PS1 for colony-forming ability, we used two types of human PS1 mutants: one (hPS1D257A) with the aspartate to alanine mutation at residue 257 that impairs the proteolytic activity of PS1, and the other (hPS1Deltacat) deleting amino acids 340-371 of the cytosolic loop sequence essential for beta-catenin binding. hPS1D257A showed activity to regulate the colony-forming ability of PS1-deficient EPC, while hPS1Deltacat failed to exhibit this activity. These results suggest that PS1 regulates the growth and differentiation of endothelial progenitor cells through its beta-catenin-binding region and that the defect of PS1 function in endothelial cell lineage could contribute to the induction of vascular pathology.

Animals↗
PubMed2005

Formation and stabilization model of the 42-mer Abeta radical: implications for the long-lasting oxidative stress in Alzheimer's disease.

Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40.

Alzheimer Disease↗
PubMed2005

Verification of the turn at positions 22 and 23 of the beta-amyloid fibrils with Italian mutation using solid-state NMR.

The aggregation of 42-mer amyloid beta (Abeta42) plays a central role in the pathogenesis of Alzheimer's disease. Our recent research on proline mutagenesis of Abeta42 suggested that the formation of a turn structure at positions 22 and 23 could play a crucial role in its aggregative ability and neurotoxicity. Since E22K-Abeta42 (Italian mutation) aggregated more rapidly and with more potent neurotoxicity than wild-type Abeta42, the tertiary structure at positions 21-24 of E22K-Abeta42 fibrils was analyzed by solid-state NMR using dipolar-assisted rotational resonance (DARR) to identify the 'malignant' conformation of Abeta42. Two sets of chemical shifts for Asp-23 were observed in a ratio of about 2.6:1. The 2D DARR spectra at the mixing time of 500 ms suggested that the side chains of Asp-23 and Val-24 in the major conformer, and those of Lys-22 and Asp-23 in the minor conformer could be located on the same side, respectively. These data support the presence of a turn structure at positions 22 and 23 in E22K-Abeta42 fibrils. The formation of a salt bridge between Lys-22 and Asp-23 in the minor conformer might be a reason why E22K-Abeta42 is more pathogenic than wild-type Abeta42.

Amino Acid Sequence↗
PubMed2005

Tissue hyperoxygenation promotes oxidative metabolism in motor unit.

Some mutant hemoglobin (Hb) variants are found with lowered O2 affinity. Low oxygen affinity is reported to increase the O2 availability in peripheral tissues (Kunert et al. [1996] Microvasc. Res. 52:58-68). In the present study, we used a mouse model carrying two low-affinity Hb variants, Titusville and Presbyterian, to evaluate the chronic in vivo influence of lowered oxygen affinity on the neuromuscular system. Our model mice showed an increased voluntary running ability compared with wild-type littermates. In the tibialis anterior (TA) muscle of mutant mice, the glycolytic fibers were converted to oxidative ones in where the activity of the mitochondrial marker enzyme succinate dehydrogenase (SDH) was up-regulated. We report that the spinal ventral horn motoneurons innervating TA skeletal fibers also showed higher mitochondrial oxidative enzyme activity. This phenomenon was evidenced by increased SDH activity and electron microscopic (EM) mitochondrial electronic density in these motoneurons. Our data suggest that, as the result of adaptation to the tissue hyperoxygenation, energy metabolism in the neuron-muscle motor unit is augmented and thus function of the motor unit is promoted.

Adenosine Triphosphatases↗
PubMed2005

Estrogen, insulin, and dietary signals cooperatively regulate longevity signals to enhance resistance to oxidative stress in mice.

To investigate the biological significance of a longevity mutation found in daf-2 of Caenorhabditis elegans, we generated a homologous murine model by replacing Pro-1195 of insulin receptors with Leu using a targeted knock-in strategy. Homozygous mice died in the neonatal stage from diabetic ketoacidosis, whereas heterozygous mice showed the suppressed kinase activity of the insulin receptor but grew normally without spontaneously developing diabetes during adulthood. We examined heterozygous insulin receptor mutant mice for longevity phenotypes. Under 80% oxygen, mutant female mice survived 33.3% longer than wild-type female mice, whereas mutant male mice survived 18.2% longer than wild-type male mice. These results suggested that mutant mice acquired more resistance to oxidative stress, but the benefit of the longevity mutation was more pronounced in females than males. Manganese superoxide dismutase activity in mutant mice was significantly upregulated, suggesting that the suppressed insulin signaling leads to an enhanced antioxidant defense. To analyze the molecular basis of the gender difference, we administered estrogen to mutant mice. It was found that the survival of mice under 80% oxygen was extended when they were administered estradiol. In contrast, mutant and wild-type female mice showed shortened survivals when their ovaries were removed. The influence of estrogen is remarkable in mutant mice compared with wild-type mice, suggesting that estrogen modulates insulin signaling in mutant mice. Furthermore, we showed additional extension of survival under oxidative conditions when their diet was restricted. Collectively, we show that three distinct signals; insulin, estrogen, and dietary signals work in independent and cooperative ways to enhance the resistance to oxidative stress in mice.

Animals↗
PubMed2005

Beneficial effect of transfusion with low-affinity red blood cells in endotoxemia.

BACKGROUND: Sepsis caused by endotoxins such as lipopolysaccharide (LPS) impairs the microcirculation, diminishing tissue blood supply and aggravates systemic hypoxia. A novel lower-affinity hemoglobin (Hb) variant, Hb Presbyterian, enhances oxygen release to peripheral tissues and may improve tissue oxygen supply during sepsis. STUDY DESIGN AND METHODS: This study investigated the effectiveness of Presbyterian Hb in transfusion therapy with LPS-challenged sepsis mouse model. Septic wild-type mice were transfused with RBCs from Presbyterian Hb-carrying mutant mice and wild-type mice. Their survival rates were assessed, and apoptosis of hepatocytes was evaluated. Survival rates of septic Presbyterian mutant mice and the wild-type littermates were also studied. RESULTS: The Presbyterian mutant RBC-transfused septic group survived longer than the wild-type RBC-transfused group. Apoptosis was reduced in the hepatocytes of the former group. Presbyterian mutant mice themselves, however, did not have stronger resistance to LPS-induced sepsis. CONCLUSION: Transfusion of low-affinity Hb-containing RBCs has beneficial effects in septic mice.

Animals↗
PubMed2005

Biological significance of isoaspartate and its repair system.

Isomerization of L-aspartate and deamidation of L-asparagine in proteins or peptides dominantly give rise to L-isoaspartate by a non-enzymatic reaction via succinimide as a intermediate under physiological conditions. Isoaspartates have been identified in a variety of cellular proteins in vivo as well as pathologically deposited proteins in neurodegenerative brain tissue. We described here that the formation of isoaspartate is enhanced in amyloid-beta (Abeta) peptides in Alzheimer's disease (AD). Specific antibodies recognizing isoaspartate of Abeta revealed that isomerized Abeta peptides were deposited in senile plaques as well as amyloid-bearing vessels. Moreover, it was revealed that Abeta peptides, isomerized at position 7 or 23, were differentially deposited in senile plaques and vascular amyloids in AD brains. In vitro experiments showed that the modification at position 23 greatly enhanced the aggregation of Abeta. Furthermore, systematic proline substitution analyses revealed that the beta-turn structure at positions 22 and 23 of Abeta42 plays a crucial role in the aggregation and neurotoxicity of Abeta peptides. It is suggested that spontaneous isomerization at position 23 induces the conformational change to form a beta-turn at position 23, which plays a pathogenic role in the deposition of Abeta peptides in sporadic AD. Protein L-isoaspartyl methyltransferase (PIMT) is a putative protein repair enzyme, which converts L-isoaspartyl residues in damaged proteins to normal L-aspartyl residues. PIMT-deficient mice manifested neurodegenerative changes concomitant with the accumulation of L-isoaspartate in the brain. We discuss here the pathological implications of the formation of isoaspartate in damaged proteins during neurodegeneration in model mice and AD.

Alzheimer Disease↗
PubMed2005

Structure of beta-amyloid fibrils and its relevance to their neurotoxicity: implications for the pathogenesis of Alzheimer's disease.

Alzheimer's disease and cerebral amyloid angiopathy are characterized by the deposition of beta-amyloid fibrils consisting of 40- and 42-mer peptides (A beta 40 and A beta 42). Since the aggregation (fibrilization) of these peptides is closely related to the pathogenesis of these diseases, numerous structural analyses of A beta 40 and A beta 42 fibrils have been carried out. A beta 42 plays a more important role in the pathogenesis of these diseases since its aggregative ability and neurotoxicity are considerably greater than those of A beta 40. This review summarizes mainly our own recent findings from the structural analysis of A beta 42 fibrils and discusses its relevance to their neurotoxicity in vitro.

Alzheimer Disease↗
PubMed2004

Analysis of the secondary structure of beta-amyloid (Abeta42) fibrils by systematic proline replacement.

Amyloid fibrils in Alzheimer's disease mainly consist of 40- and 42-mer beta-amyloid peptides (Abeta40 and Abeta42) that exhibit aggregative ability and neurotoxicity. Although the aggregates of Abeta peptides are rich in intermolecular beta-sheet, the precise secondary structure of Abeta in the aggregates remains unclear. To identify the amino acid residues involved in the beta-sheet formation, 34 proline-substituted mutants of Abeta42 were synthesized and their aggregative ability and neurotoxicity on PC12 cells were examined. Prolines are rarely present in beta-sheet, whereas they are easily accommodated in beta-turn as a Pro-X corner. Among the mutants at positions 15-32, only E22P-Abeta42 extensively aggregated with stronger neurotoxicity than wild-type Abeta42, suggesting that the residues at positions 15-21 and 24-32 are involved in the beta-sheet and that the turn at positions 22 and 23 plays a crucial role in the aggregation and neurotoxicity of Abeta42. The C-terminal proline mutants (A42P-, I41P-, and V40P-Abeta42) hardly aggregated with extremely weak cytotoxicity, whereas the C-terminal threonine mutants (A42T- and I41T-Abeta42) aggregated potently with significant cytotoxicity. These results indicate that the hydrophobicity of the C-terminal two residues of Abeta42 is not related to its aggregative ability and neurotoxicity, rather the C-terminal three residues adopt the beta-sheet. These results demonstrate well the large difference in aggregative ability and neurotoxicity between Abeta42 and Abeta40. In contrast, the proline mutants at the N-terminal 13 residues showed potent aggregative ability and neurotoxicity similar to those of wild-type Abeta42. The identification of the beta-sheet region of Abeta42 is a basis for designing new aggregation inhibitors of Abeta peptides.

Alzheimer Disease↗
PubMed2004

Presenilin 1 is essential for cardiac morphogenesis.

Presenilin 1 (PS1) is the gene responsible for the development of early-onset familial Alzheimer's disease. PS1-deficient mice have been reported to show defects in neurogenesis, somitogenesis and angiogenesis. Here, we report cardiac anomaly in PS1-deficient mice: the mutant hearts exhibited ventricular septal defect, double outlet right ventricle, and stenosis in the pulmonary artery. Immunohistochemistry using anti-PS1 antibody revealed the prominent expression of PS1 in mesenchymal cells at the septal area of the wild-type heart. These results suggest that PS1 may play an essential role in heart development.

Animals↗