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Biomedical subjects

Hiroki Kurihara

Publications and source records attributed to Hiroki Kurihara.

At least 37 records · Page 2Linked to original sources
PubMed2004

Differential cooperation between dHAND and three different E-proteins.

dHAND is a transcription factor belonging to the class B basic helix-loop-helix protein family and is expressed during embryogenesis in the heart, branchial arches, limb buds, and neural crest derivatives. Despite much study, the molecular mechanisms involved in the regulation of dHAND activity are not well understood. We therefore carried out yeast two-hybrid screening using full-length dHAND as bait, which led to identification of several dHAND-binding proteins, including three E-proteins: E2A, ME2, and ALF1. Subsequent analysis revealed that although their heterodimerization and transcriptional activities were similar, dHAND/E-protein heterodimers bind to an E-box element with differing affinities, suggesting they have distinct DNA binding specificities. Moreover, in situ hybridization showed that E-protein genes are expressed fairly ubiquitously among embryonic tissues, including the branchial arches and limb buds. By contrast, little signal was detected in the heart, suggesting that dHAND complexes with partners other than E-proteins in cardiac tissue.

Animals↗
PubMed2004

Endothelin-1 regulates the dorsoventral branchial arch patterning in mice.

Endothelin-1 (ET-1), a 21-amino acid peptide secreted by the epithelium and core mesenchyme in the branchial arches as well as vascular endothelium, is involved in craniofacial and cardiovascular development through endothelin receptor type-A (EdnrA) expressed in the neural crest-derived ectomesenchyme. Here we show that ET-1(-/-) mutant mice exhibit a homeotic-like transformation of the lower jaw to an upper jaw. Most of the maxillary arch-derived components are duplicated and replaced mandibular arch-derived structures, resulting in a mirror image of the upper and lower jaws in the ET-1(-/-) mutant. As for hyoid arch-derivatives, the ventral structures are severely affected in comparison to the dorsal ones in the ET-1(-/-) mutant. Correspondingly, the expression of Dlx5 and Dlx6, Distalless-related homeobox genes determining the ventral identity of the anterior branchial arches, and of the mandibular marker gene Pitx1 is significantly downregulated in the ET-1(-/-) mutant, whereas the expression of Dlx2 and the maxillary marker gene Prx2 is unaffected or rather upregulated. These findings indicate that the ET-1/EdnrA signaling may contribute to the dorsoventral axis patterning of the branchial arch system as a mediator of the regional intercellular interactions.

Animals↗
PubMed2004

Temporal requirement of signaling cascade involving endothelin-1/endothelin receptor type A in branchial arch development.

Intercellular interactions within the branchial arch (BA) system is essential for craniofacial development. Endothelin-1 (ET-1), produced by the branchial epithelium and core mesenchyme, acts on cranial neural crest-derived ectomesenchymcal cells expressing endothelin A receptor (ETAR) and regulates expression of crucial genes such as Dlx6, a member of distalless homeobox gene family, and its downstream target dHAND, a basic helix-loop-helix transcription factor. To investigate the role of ET-1 and subsequent signaling cascades in BA development, we examined when and how they activate dHAND and Dlx6 expression. ETAR blockade by BQ123 in mouse embryo culture has revealed that ET-1/ETAR signaling is critical for dHAND and Dlx6 expression in the mandibular arch mesenchyme around embryonic day (E)8.75-E9.0 and becomes dispensable by E9.5. dHAND and Dlx6 expression after E9.5 was dependent on the presence of the epithelium, which was partly mediated by FGF-like signals. These findings indicate that ET-1/ETAR and subsequent epithelial signals are sequentially involved in BA development by maintaining dHAND and Dlx6 expression. Furthermore, discordance of dHAND and Dlx6 expression domains and heterogeneity with respect to dependency on ET-1 and FGF-like signals suggest that genetic hierarchy involving Dlx6 and dHAND is differently controlled among subdomains within the mandibular arch.

Animals↗
PubMed2004

Akt-dependent phosphorylation negatively regulates the transcriptional activity of dHAND by inhibiting the DNA binding activity.

HAND2/dHAND is a basic helix-loop-helix transcription factor expressed in the heart and neural crest derivatives during embryogenesis. Although dHAND is essential for branchial arch, cardiovascular and limb development, its target genes have not been identified. The regulatory mechanisms of dHAND function also remain relatively unknown. Here we report that Akt/PKB, a serine/threonine protein kinase involved in cell survival, growth and differentiation, phosphorylates dHAND and inhibits dHAND-mediated transcription. AU5-dHAND expressed in 293T cells became phosphorylated, possibly at its Akt phosphorylation motif, in the absence of kinase inhibitors, whereas the phosphatidylinositol 3-kinase inhibitor wortmannin and the Akt inhibitor NL-71-101, but not the p70 S6 kinase inhibitor rapamycin, significantly reduced dHAND phosphorylation. Coexpression of HA-Akt augmented dHAND phosphorylation at multiple serine and threonine residues mainly located in the bHLH domain and, as a result, decreased the transcriptional activity of dHAND. Consistently, alanine mutation mimicking the nonphosphorylation state abolished the inhibitory effect of Akt on dHAND, whereas aspartate mutation mimicking the phosphorylation state resulted in a loss of dHAND transcriptional activity. These changes in dHAND transcriptional activity were in parallel with changes in the DNA binding activity rather than in dimerization activity. These results suggest that Akt-mediated signaling may regulate dHAND transcriptional activity through the modulation of its DNA binding activity during embryogenesis.

Amino Acid Sequence↗
PubMed2004

Endothelin-1 regulates cardiac sympathetic innervation in the rodent heart by controlling nerve growth factor expression.

The cardiac sympathetic nerve plays an important role in regulating cardiac function, and nerve growth factor (NGF) contributes to its development and maintenance. However, little is known about the molecular mechanisms that regulate NGF expression and sympathetic innervation of the heart. In an effort to identify regulators of NGF in cardiomyocytes, we found that endothelin-1 specifically upregulated NGF expression in primary cultured cardiomyocytes. Endothelin-1-induced NGF augmentation was mediated by the endothelin-A receptor, Gibetagamma, PKC, the Src family, EGFR, extracellular signal-regulated kinase, p38MAPK, activator protein-1, and the CCAAT/enhancer-binding protein delta element. Either conditioned medium or coculture with endothelin-1-stimulated cardiomyocytes caused NGF-mediated PC12 cell differentiation. NGF expression, cardiac sympathetic innervation, and norepinephrine concentration were specifically reduced in endothelin-1-deficient mouse hearts, but not in angiotensinogen-deficient mice. In endothelin-1-deficient mice the sympathetic stellate ganglia exhibited excess apoptosis and displayed loss of neurons at the late embryonic stage. Furthermore, cardiac-specific overexpression of NGF in endothelin-1-deficient mice overcame the reduced sympathetic innervation and loss of stellate ganglia neurons. These findings indicate that endothelin-1 regulates NGF expression in cardiomyocytes and plays a critical role in sympathetic innervation of the heart.

Animals↗
PubMed2004

Glucose transporter and Na+/glucose cotransporter as molecular targets of anti-diabetic drugs.

Glucose transporters, or membrane proteins, which incorporate glucose into the cell, can be divided into two groups: the facilitative type glucose transporter (GLUT), and the sodium/glucose cotransporter (SGLT). Among the GLUT family isoforms, GLUT4 is particularly important for maintaining glucose metabolism homeostasis since it is involved in insulin or exercise-induced glucose transport into muscle and adipose tissues via movement from intracellular sites to the plasma membrane in response to stimulation. Thus, agents which induce GLUT4 translocation or improve insulin sensitivity, involved in this insulin-induced step, hold the promise of being potent anti-diabetic drugs. On the other hand, SGLT is expressed specifically in the intestines and kidneys. Oral administration of a SGLT inhibitor, T-1095, lowers the blood glucose concentration via excretion of glucose in the urine, due to suppression of renal SGLT function. In addition to this direct blood glucose lowering effect, T-1095 has been shown to restore impaired insulin secretion from pancreatic beta-cells, as well as to improve insulin resistance in muscle and liver. Thus, this SGLT inhibitor is regarded as a novel and promising agent for the treatment of diabetes mellitus.

Animals↗
PubMed2003

Ephrin-B2 induces migration of endothelial cells through the phosphatidylinositol-3 kinase pathway and promotes angiogenesis in adult vasculature.

OBJECTIVE: Ephrin-B2 plays a key role in vascular development. The purpose of this study was to elucidate the molecular mechanisms of ephrin-B2 signaling through the EphB receptor in endothelial cells and to determine whether ephrin-B2 contributes to in vivo angiogenesis in adult mice. METHODS AND RESULTS: A chemotaxis assay on a polycarbonate membrane revealed that ephrin-B2/Fc chimeric protein induced migration of human umbilical vein endothelial cells (HUVECs) at a level 98% greater than control (P<0.01). To determine the signaling pathways activated in the HUVECs by Eph stimulation, phosphatidylinositol-3 kinase (PI3 kinase) activity was determined in an immune complex PI3 kinase assay. Serum-starved HUVECs were stimulated with ephrin-B2/Fc and compared with unstimulated cells. PI3 kinase activity in stimulated cells was higher than that seen in unstimulated cells. In a chemotaxis assay, the PI3 kinase-specific inhibitor LY294002 blocked the migratory response of HUVECs induced by addition of ephrin-B2/Fc. Finally, ephrin-B2/Fc promoted angiogenesis in vivo in corneal neovascularization and Matrigel plug assays in adult mice, whereas LY294002 reduced angiogenesis in Matrigel that was induced by ephrin-B2/Fc. CONCLUSIONS: Ephrin-B2/Fc induces the migration of HUVECs through the PI3 kinase signaling pathway. Ephrin-B2/Fc promotes in vivo angiogenesis in adult mice, suggesting that it contributes to adult angiogenesis.

Animals↗
PubMed2003

Structural and functional characterization of gastric mucosa and central nervous system in histamine H2 receptor-null mice.

To examine the physiological role of the histamine H(2) receptor, histamine H(2) receptor-null mice were generated by homologous recombination. Histamine H(2) receptor-null mice, which developed normally and were fertile and healthy into adulthood, exhibited markedly enlarged stomachs and marked hypergastrinemia. The former was due to hyperplasia of gastric gland cells (small-sized parietal cells, enterochromaffin-like cells and mucous neck cells which were rich in mucin), but not of gastric surface mucous cells, which were not increased in number as compared with those in wild-type mice despite the marked hypergastrinemia. Basal gastric pH was slightly but significantly higher in histamine H(2) receptor-null mice. Although carbachol but not gastrin induced in vivo gastric acid production in histamine H(2) receptor-null mice, gastric pH was elevated by both muscarinic M(3) and gastrin antagonists. Thus, both gastrin and muscarinic receptors appear to be directly involved in maintaining gastric pH in histamine H(2) receptor-null mice. Interestingly, gastric glands from wild-type mice treated with an extremely high dose of subcutaneous lansoprazole (10 mg/kg body weight) for 3 months were very similar to those from histamine H(2) receptor-null mice. Except for hyperplasia of gastric surface mucous cells, the findings for gastric glands from lansoprazole-treated wild-type mice were almost identical to those from gastric glands from histamine H(2) receptor-null mice. Therefore, it is possible that the abnormal gastric glands in histamine H(2) receptor-null mice are secondary to the severe impairment of gastric acid production, induced by the histamine H(2) receptor disruption causing marked hypergastrinemia. Analyses of the central nervous system (CNS) of histamine H(2) receptor-null mice revealed these mice to be different from wild-type mice in terms of spontaneous locomotor activity and higher thresholds for electrically induced convulsions. Taken together, these results suggest that (1) gastrin receptors are functional in parietal cells in histamine H(2) receptor-null mice, (2) abnormal gastric glands in histamine H(2) receptor-null mice may be secondary to severe impairment of gastric acid production and secretion and (3) histamine H(2) receptors are functional in the central nervous system.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed2003

Inhibitory effect of natriuretic peptides on aldosterone synthase gene expression in cultured neonatal rat cardiocytes.

BACKGROUND: Although previously thought to be synthesized solely in adrenal cortex, we have recently showed that aldosterone is also produced in and the expression of CYP11B2 mRNA was induced in the failing or hypertensive human ventricle. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones with wide biological effects, including inhibition of renin and aldosterone production. We hypothesized that natriuretic peptides reduce the expression of CYP11B2 mRNA in the heart. METHODS AND RESULTS: To test this hypothesis, we examined whether endogenous or exogenous natriuretic peptides reduce the expression of CYP11B2 mRNA using real-time reverse transcription-polymerase chain reaction. By using HS 142-1, a functional guanylyl cyclase-A type receptor antagonist, we showed that angiotensin II (AngII) pretreated with HS 142-1 increased CYP11B2 mRNA expression (1.62+/-0.12-fold, HS 142-1+AngII 10(-7) mol/L versus AngII 10(-7) mol/L alone, P<0.0001). The treatment with exogenous (10(-6) mol/L) ANP and BNP reduced CYP11B2 mRNA expression (ANP, P=0.0042; BNP, P=0.0012). CONCLUSIONS: We showed that endogenous and exogenous natriuretic peptides reduced CYP11B2 mRNA expression in cultured neonatal rat cardiocytes. This may inhibit the cardiac renin-angiotensin-aldosterone system by suppressing the gene expression of CYP11B2 and restraining cardiac hypertrophy and fibrosis.

Angiotensin II↗
PubMed2003

Targeted disruption of adrenomedullin and alphaCGRP genes reveals their distinct biological roles.

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) share common structural characteristics and receptors and belong to the same peptide family. Both peptides show a diverse set of biological effects including vasodilation. Recent establishment of gene-knockout mice has revealed the physiological importance of these two peptides. AM -/- mice demonstrated defective vascular formation during embryogenesis and did not survive beyond midgestation. AM +/- heterozygous mice showed high blood pressure and susceptibility to tissue injury. On the other hand, alphaCGRP -/- mice demonstrated elevated peripheral vascular resistance and high blood pressure caused by increased peripheral sympathetic activity. Thus, AM and CGRP have distinct physiological roles. AM is indispensable for normal embryonic development, regulation of blood pressure and tissue protection against injury, whereas alphaCGRP contributes to the regulation of cardiovascular function through inhibitory modulation of sympathetic nervous activity.

Adrenomedullin↗
PubMed2003

Endothelial responses of the aorta from adrenomedullin transgenic mice and knockout mice.

Adrenomedullin (AM) is a potent vascular wall-derived vasorelaxing peptide which induces the release of nitric oxide (NO). To explore the role of endogenous AM in vascular function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists [AM (22-52), and calcitonin gene-related peptide (CGRP) (8-37)] on the isometric tension of aortic rings isolated from AM transgenic (TG) and knockout (KO) mice and wild type littermates (WT). ACh and AM caused a dose-dependent reduction of the isometric tension of aortic rings, but the degree of vasodilatation was smaller in TG than in KO or WT (% delta tension [10(-6) mol/l ACh]: KO -69 +/- 10%, WT -39 +/- 8%, TG -29 +/- 1%, p < 0.01). On the other hand, N(G)-nitro-L-arginine methyl ester, an NO synthase inhibitor, induced greater vasoconstriction in TG (% delta tension 10(-5)mol/l: KO +78 +/- 16%, WT +99 +/- 27%, TG +184 +/- 20%, p < 0.01), whereas E-4021, a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase inhibitor, caused greater vasodilation in TG mice. Both AM antagonists increased tension in TG to a greater extent than in KO or WT mice (% delta tension [10(-6) mol/l CGRP (8-37)]: KO +24 +/- 5%, WT +51 +/- 6%, TG +75 +/- 7%, p < 0.01). Endothelial denudation of the aorta diminished the vasoconstriction caused by the AM antagonists. In conclusion, the amounts of AM expressed in the aortic endothelium influenced baseline NO release. AM antagonists increased vascular tone in WT as well as in TG, suggesting that endogenous AM plays a physiological role in the regulation of aortic tone.

Acetylcholine↗
PubMed2002

Identification of multiple novel epididymis-specific beta-defensin isoforms in humans and mice.

Defensins comprise a family of cationic antimicrobial peptides that are characterized by the presence of six conserved cysteine residues. We identified two novel human beta-defensin (hBD) isoforms by mining the public human genomic sequences. The predicted peptides conserve the six-cysteine motif identical with hBD-4, termed hBD-5 and hBD-6. We also evaluated the characteristics of the mouse homologs of hBD-5, hBD-6, and HE2beta1, termed mouse beta-defensin (mBD)-12, mBD-11, and mouse EP2e (mEP2e). The mBD-12 synthetic peptide showed salt-dependent antimicrobial activity. We demonstrate the epididymis-specific expression pattern of hBD-5, hBD-6, mBD-11, mBD-12, and mEP2e. In situ hybridization revealed mBD-11, mBD-12, and mEP2e expression in the columnar epithelium of the caput epididymis, contrasting with the predominant expression of mBD-3 in the capsule or septum of the whole epididymis. In addition, the regional specificity of mBD-11, mBD-12, and mEP2e was somewhat overlapping, but not identical, in the caput epididymis, suggesting that specific regulation may work for each member of the beta-defensin family. Our findings indicated that multiple beta-defensin isoforms specifically and cooperatively contribute to the innate immunity of the urogenital system.

Amino Acid Sequence↗
PubMed2002

Resistance to neointimal hyperplasia and fatty streak formation in mice with adrenomedullin overexpression.

OBJECTIVE: Several in vitro studies have implicated that adrenomedullin (AM) plays an important role in the pathogenesis of vascular injury and fatty streak formation. To test this possibility in vivo, we evaluated 2 experimental models using transgenic mice overexpressing AM in a vessel-selective manner (AMTg mice). METHODS AND RESULTS: Placement of a periarterial cuff on femoral arteries resulted in neointimal formation at 2 to 4 weeks to a lesser extent in AMTg mice than in their wild-type littermates (at 28 days, intima/media area ratio 0.45+/-0.14 versus 1.31+/-0.41, respectively; P<0.001). This vasculoprotective effect observed in AMTg mice was inhibited by N(omega)-nitro-L-arginine methyl ester. We further examined the effect of AM on hypercholesterolemia-induced fatty streak formation by crossing AMTg mice with apolipoprotein E knockout mice (ApoEKO mice). The extent of the formation of fatty streak lesions was significantly less in ApoEKO/AMTg mice than in ApoEKO mice (percent lesion area 12.0+/-3.9% versus 15.8+/-2.8%, respectively; P<0.05). Moreover, endothelium-dependent vasodilatation as indicative of NO production was superior in AMTg/ApoEKO mice compared with ApoEKO mice. CONCLUSIONS: Taken together, our data demonstrated that AM possesses a vasculoprotective effect in vivo, which is at least partially mediated by NO.

Adipose Tissue↗
PubMed2002

Role of endogenous adrenomedullin in the regulation of vascular tone and ischemic renal injury: studies on transgenic/knockout mice of adrenomedullin gene.

Adrenomedullin (AM) is a potent depressor peptide whose vascular action is suggested to involve nitric oxide (NO) release. To explore the role of endogenous AM in vascular and renal function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists AM(22-52) and CGRP(8-37) on the renal perfusion pressure (RPP) of kidneys isolated from AM transgenic (TG)/heterozygote knockout (KO) mice and wild-type littermates (WT). Furthermore, we evaluated the renal function and histology 24 hours after bilateral renal artery clamp for 45 minutes in TG, KO, and WT mice. Baseline RPP was significantly lower in TG than in KO and WT mice (KO 93.4+/-4.6, WT 85.8+/-4.2, TG 72.4+/-2.4 mm Hg [mean+/-SE], P<0.01). ACh and AM caused a dose-related reduction in RPP, but the degree of vasodilatation was smaller in TG than that in KO and WT (%DeltaRPP 10(-7) mol/L ACh: KO -48.1+/-3.9%, WT -57.5+/-5.6%, TG -22.8+/-4.8%, P<0.01), whereas N(G)-nitro-L-arginine methyl ester (L-NAME) caused greater vasoconstriction in TG (%DeltaRPP 10(-4) mol/L: KO 33.1+/-3.3%, WT 55.5+/-7.2%, TG 152.6+/-21.2%, P<0.01). Both AM antagonists increased RPP in TG to a greater extent compared with KO and WT mice (%DeltaRPP 10(-6) mol/L CGRP(8-37): KO 12.8+/-2.6%, WT 19.4+/-3.6%, TG 41.8+/-8.7%, P<0.01). In mice with ischemic kidneys, serum levels of urea nitrogen and renal damage scores showed smaller values in TG and greater values in KO mice (urea nitrogen: KO 104+/-5>WT 98+/-15>TG 38+/-7 mg/dL, P<0.05 each). Renal NO synthase activity was also greater in TG mice. However, the differences in serum urea nitrogen and renal damage scores among the 3 groups of mice were not observed in mice pretreated with L-NAME. In conclusion, AM antagonists increased renal vascular tone in WT as well as in TG, suggesting that endogenous AM plays a role in the physiological regulation of the vascular tone. AM is likely to protect renal tissues from ischemia/reperfusion injury through its NO releasing activity.

Acetylcholine↗
PubMed2002

Evaluation of the atrial natriuretic peptide gene in stroke.

The atrial natriuretic peptide (ANP) gene was, though inconclusive, implied to be etiologically related to stroke in rats and recently in humans. The present study tested the candidacy of ANP for stroke susceptibility by a combination of molecular genetic approaches. First, we undertook an association study using a reported ANP variant, G664A, in two case-control panels independently collected, which involved 970 Japanese subjects. Second, we compared the rat ANP gene sequences and neighboring marker alleles among stroke-prone SHR (SHRSP), normal SHR and WKY of an original inbred colony and we also compared brain ANP expression between SHRSP and normal SHR. In humans, we found no significant association between the 664A variant and stroke in the studied population. In rats, 21 polymorphic sites were identified by direct sequencing of 2170-bp ANP fragments, from which two distinct alleles, SHRSP- and WKY-types, were inferred. From a genealogical point of view, our data indicated that an SHRSP-type allele could not play a determinant role in stroke-proneness. Overall results did not support the disease relevance of ANP, disagreeing with previous reports. Thus, considerable caution should be taken when one attempts to transfer findings in the animal model to humans.

Aged↗
PubMed2002

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-1 null mutant mice develop renal lesions mimicking obstructive nephropathy.

BACKGROUND: A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-1 is distinguished from other a disintegrin and metalloproteinase molecules by the presence of thrombospondin type 1 motifs at its C-terminus and anchors to the extracellular matrix. We studied the biological role of ADAMTS-1 in the kidney. METHODS: We developed ADAMTS-1 null mice by replacing exons 2-4, which encode most of the metalloproteinase domain, with the neomycin resistance gene. RESULTS: In normal mice, ADAMTS-1 was detected in the epithelial cells of collecting ducts, and more intensely in the urinary epithelium at the ureteropelvic junction in kidney. We found that targeted disruption of the mouse ADAMTS-1 gene resulted in enlarged renal calices accompanied by bilateral hydronephrosis and papillary atrophy approximately 4 weeks after birth. Electron microscopic examination revealed the fibrotic changes and hypervascularity of capillaries between the urinary epithelial cell layer and smooth muscle cell layer at the ureteropelvic junction. CONCLUSION: ADAMTS-1 appears necessary for normal kidney morphology and function. Moreover, the resemblance of the renal phenotype to human ureteropelvic junction obstruction may provide a clue to the pathogenesis of this common congenital disease.

ADAM Proteins↗