Relógios biológicos são marcapassos endógenos presentes tanto em eucariotos quanto em procariotos. Relógios diferentes possuem períodos distintos, e aqueles que se aproximam de 24h de oscilação são chamados circadianos. Em mamíferos, o primeiro relógio circadiano identificado situa-se no núcleo supraquiasmático, localizado no hipotálamo. O funcionamento do relógio circadiano envolve mecanismos de retroalimentação positiva e negativa, em geral tendo início com a ativação dos genes Per e Cry por CLOCK e BMAL1. Atualmente sabe-se que os relógios estão presentes em áreas do cérebro fora do núcleo supraquiasmático e em muitos tecidos periféricos. Em Drosophila e Danio rerio, os osciladores periféricos podem ser sincronizados diretamente por luz, enquanto em mamíferos o reinício de fase dos mesmos parece ser controlado por sinais regulados pelo marcapasso do núcleo supraquiasmático. Uma nova opsina, denominada melanopsina, foi recentemente descoberta na retina de todos os vertebrados estudados, em uma subpopulação de células ganglionares intrinsecamente fotossensíveis. Ela é responsável pela captura de luz e envio dessa informação para o núcleo supraquiasmático. A endotelina (ET) é um peptídeo vasoconstritor composto por 21 resíduos de aminoácidos. Existem três isoformas endógenas de ETs, designadas ET-1, ET-2 e ET-3. Três tipos de receptores para endotelinas já foram clonados, sendo eles designados ETA, ETB e ETC. Todos pertencem à família dos receptores acoplados à proteína G. Órgãos, tecidos e células de Danio rerio constituem um excelente modelo para o estudo dos genes de relógio e de ritmos in vitro. Em células embrionárias ZEM 2S deste teleósteo, constatamos a presença de melanopsina, do receptor ETA para endotelina, e dos seis genes Cry através de PCR. A presença de melanopsina também foi confirmada por imunocitoquímica. Foram realizadas curvas de crescimento em células ZEM 2S previamente mantidas por cinco dias em regime de 14C:10E (luz acesa às 9:00h). No 6º. dia, as células foram transferidas para as seguintes condições: escuro constante; 14C:10E; 10C:14E e luz constante. Houve inibição da proliferação celular por luz. O padrão de expressão temporal dos genes Per1, Cry1b, Clock e da melanopsina foi estudado, assim como sua modulação por ET-1. Células ZEM 2S foram mantidas em fotoperíodo 12C:12E (luz acesa às 9:00h) durante cinco dias, após o que foram tratadas com ET-1 nas concentrações 10-11M, 10-10M, 10-9M e 10-8M, durante 24h. O RNA extraído a cada 3h foi submetido a RT-PCR para posterior análise por PCR quantitativo. RNA ribossômico 18S foi utilizado como normalizador do experimento. Melanopsina não apresentou ritmicidade de expressão em fotoperíodo 12C:12E. ET-1 exerceu efeito bifásico, aumentando a expressão nas menores concentrações de hormônio utilizadas e diminuindo nas maiores. Na concentração 10-10M, ET-1 aparentemente estabeleceu uma oscilação ao longo das 24 horas, com crescente expressão na fase de escuro, atingindo um pico em ZT21 e decrescente durante o período de luz, com o mínimo em ZTs 6 e 9. A expressão do gene Clock é rítmica em regime fotoperíodo 12C:12E, com valores significativamente maiores em ZT12 a ZT21 do que em ZT0, ZT3 e ZT9, indicando um aumento de expressão coincidente com o período de escuro. Foi observado um pico de expressão em ZT6, durante a fase de luz. ET-1 nas concentrações de 10-11 e 10-10M aboliu o ritmo de expressão de Clock, e inibiu o pico de expressão em ZT6. Expressão de Clock permaneceu elevada somente em ZT18. Nas maiores concentrações (10-9M e 10-8M), a inibição ocorreu em todos os ZTs, abolindo completamente o ritmo e atenuando qualquer variação previamente observada entre os ZTs. A expressão do gene Per1 é rítmica em regime fotoperíodo 12C:12E, com valores significativamente maiores nos ZTs 21, 0, 3, 6 e 9 do que nos ZTs 12, 15 e 18, indicando um aumento de expressão na fase de claro. Vale mencionar que já em ZT21, há um aumento significativo antecipatório da fase de luz. Nas concentrações de 10-11 e 10-10M, ET-1 não alterou o período ou a amplitude desse ritmo. A ação evidente de ET-1 foi a inibição da expressão de Per1 na fase de luz (ZT0, ZT3, ZT6 e ZT9), e também em ZT21 (fase de escuro) nas maiores concentrações (10-9M e 10-8M) não afetando o período da oscilação, mas diminuindo marcadamente sua amplitude. A expressão de Cry1b foi rítmica durante o ciclo claro:escuro, com aumento na fase de claro e diminuição na fase de escuro. Novamente a ET-1 apresentou um efeito bifásico sobre a expressão deste gene, aumentando a mesma durante a fase de luz na concentração de 10-11M, e em ZT6 e ZT9 na concentração 10-10M. No entanto, não alterou o período ou a amplitude do ritmo. Por outro lado, durante toda a fase de luz houve inibição deste gene na presença de ET-1 10-9 e 10-8M, diminuindo a amplitude observada nas células controle. / Biological clocks are endogenous timekeepers that are present both in eukaryotic as in prokaryotic organisms. Different clocks have different periods, and those that have about 24h of oscillation are called circadian clocks. In mammals, the first identified circadian clock is located in the suprachiasmatic nucleus, in the hipothalamus. It is now well known that clocks are present in brain regions other than the suprachiasmatic nucleus and in many peripheral tissues. In Drosophila and Danio rerio, peripheral oscillators can be synchronized directly by light, while in mammals the reset of the phase seems to be controlled by signals regulated by the suprachiasmatic timekeepers. The maintenance of the circadian clock is governed by positive and negative feedback loops, in general starting with the activation of Per and Cry genes by CLOCK and BMAL1. A new opsin called melanopsin, was recently discovered in the retina of all studied vertebrates, in a subset of intrinsically photosensitive ganglion cells. This photopigment is responsible for capturing light and sending this information to the suprachiasmatic nucleus. Endothelin (ET) is a 21-amino acid residue vasoconstrictor peptide. There are three endogenous isoforms of ETs, ET1, ET2 and ET3. Three subtypes of endothelin receptors have already been cloned: ETA, ETB and ETC, all members of the family of G protein -coupled receptors. Organs, tissues and cells of Danio rerio constitute an excellent model for the study of clock genes and rhythms in vitro. In ZEM 2S embryonic cells of this teleost, we demonstrated the presence of melanopsin, the endothelin receptor ETA, and the six Cry genes by PCR. The presence of melanopsin was also confirmed by immunohistochemistry. ZEM 2S cells previously kept for five days in 14L:10D (lights on 9:00am) were transferred in the sixth day to the following conditions: constant darkness, 14L:10D, 10L:14D and constant light, and growth curves were determined. ZEM 2S showed inhibition of proliferation by light. The temporal expression pattern of the genes Per1, Cry1b, Clock and of melanopsin and their modulation by ET-1 were studied. ZEM 2S cells were kept in 12D:12L photoperiod (lights on 9:00am) for five days, and then treated with 10-11M, 10-10M, 10-9M and 10-8M ET-1, for 24h. RNA extracted every 3 hours was submitted to RT-PCR for subsequent analysis by Real Time-PCR. 18S ribosomal RNA was used to normalize the results. Melanopsin did not show rhythmicity of expression in 12D:12L photoperiod. ET-1 exhibited a biphasic effect, increasing the expression in the lower concentrations, and reducing at the higher concentrations. At 10-10M, ET-1 apparently established an oscillation along the 24h-period, with increasing expression in the dark phase, reaching a peak at ZT2, and decreasing during the light phase, with the minimum at ZT6 and 9. The expression of Clock gene was rhythmic in 12D:12L photoperiod, with significant higher values in ZT12 to ZT21 than ZT0, ZT3 e ZT9, indicating an increase of expression coincident with the dark period. A peak of expression was observed at ZT6, during the light phase. At 10-11 and 10-10M, ET-1 abolished the rhythm of expression of Clock, and inhibited the peak of expression at ZT6. Expression of Clock remained high only at ZT18. At the higher concentrations (10-9M e 10-8M), the inhibition occurred at all ZTs, completely abolishing the rhythm and attenuating any variation previously observed among ZTs. The expression of Per1 gene was rhythmic in 12D:12L photoperiod, with significant higher values at ZTs 21, 0, 3, 6 and 9 than at ZTs 12, 15 and 18, indicating an increase of expression in the light phase. It is important to mention that at ZT21 there was already a significant increase, anticipatory of the light phase. At 10-11 e 10-10M, ET-1 did not alter neither the period nor the amplitude of this rhythm. The evident action of ET-1 was the inhibition of Per1 expression in the light phase (ZT0, ZT3, ZT6 e ZT9), and also at ZT21 (dark phase), at the higher concentrations (10-9M e 10-8M), with no change in the oscillation period, but markedly reducing its amplitude. The expression of Cry1b was rhythimic during the light:dark cycle, with increase in the light phase and reduction in the dark phase. Again, ET-1 showed a biphasic effect on this gene expression, increasing it during the light phase at the concentration of 10-11M, and at ZT6 and 9 at 10-10M. However, the hormone did not affect either the period or the amplitude of the rhythm. On the other hand, along the light phase, there was inhibition of Cry1b in the presence of ET-1 10-9 and 10-8M, reducing the amplitude observed in the control cells.

Abstract During cardiac hypertrophy individual cardiac myocytes increase in size, which is accompanied by augmented protein synthesis and selective induction of a subset of genes. These phenotypic changes of myocytes are a result from altered intracellular signaling mechanisms and molecules. B-type natriuretic peptide (BNP) gene was selected as a target gene for the study of cardiac signaling mechanisms, since it is activated by mechanical, neural and humoral stimuli during myocyte hypertrophy. To generate hypertrophy of cardiac myocytes, neonatal rat cardiac myocytes were subjected to exogenous hypertrophic agonists such as endothelin-1 (ET-1) or to cyclic mechanical stretch. The role and regulation of transcription factors were studied by utilizing promoter analysis together with site-specific mutations and measurement of DNA binding activity and phosphorylation. GATA-4 mediated signaling was inhibited by blocking DNA binding with decoy oligonucleotides or by decreasing GATA-4 synthesis via adenoviral antisense delivery. ET-1 activated GATA-4 via serine residue phosphorylation, and this effect was mediated via p38 kinase. Similarly, GATA-4 binding activity was increased by ET-1 and mechanical stretch, but it was essential for activation of BNP gene only in the latter stimulation. Importantly, downregulation of GATA-4 protein levels prevented mechanical stretch induced hypertrophy of cardiac myocytes. In contrast, separate mechanism for an ET-1 specific signaling was composed of p38 kinase regulated ETS-like transcription factor-1 (Elk-1). Finally, the effect of mechanical stretch on endogenous endothelin-1 (ET-1) synthesis in cardiac cells was studied. Intrinsic ET-1 synthesis was activated in stretched cardiac myocytes, yet the levels of ET-1 were relatively low. This work suggests that GATA-4 transcription factor is required for mechanical stretch mediated hypertrophic program, and Elk-1 may act as a downstream effector of ET-1 in cardiac myocytes. Taken together, induction of ET-1 and BNP genes as well as activation of GATA-4 and Elk-1 transcription factors are regulated via a network of mitogen activated protein kinase pathways.

Abstract Cardiac myocytes react to increased workload and hypertrophic neurohumoral stimuli by increasing protein synthesis, reinitiating expression of fetal forms of structural genes, α-skeletal actin (α-SkA) and β-myosin heavy chain (β-MHC), and by increasing expression and secretion of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP). Initially, the response is beneficial, but when prolonged, it leads to pathological cardiomyocyte hypertrophy. In this study, cardiomyocyte hypertrophy was initiated by hypertrophic agonists, endothelin-1 (ET-1) and phenylephrine (PE), and by increased stretching of atrial wall. Transcription factor GATA4 was studied to identify the mechanism leading to increased gene expression of BNP. In BNP promoter, GATA4 binds to cis elements mediating hypertrophic response. Eliminating GATA4 binding by using the decoy approach, basal BNP gene expression was reduced. To identify mechanisms regulating GATA4, the roles of mitogen-activated protein kinases (MAPKs) were studied. Activation of p38 MAPK increased GATA4 binding to BNP gene and led to increased GATA4 dependent BNP gene expression. p38 MAPK was required for ET-1 induced GATA4 binding, whereas extracellular signal-regulated kinase (ERK) was required for maintaining basal GATA4 binding activity. PE and ET-1 activated protein kinase C (PKC) signaling in cardiac myocytes. Antisense oligonucleotide inhibition of PKCα markedly reduced PE induced ANP secretion and ET-1 induced BNP secretion, whereas gene expression of natriuretic peptides was not affected. Antisense PKCα treatment inhibited PE induced expression of α-SkA, while increased protein synthesis or β-MHC gene expression were not affected. Sretching of the perfused rat atria increased BNP, c-fos and BNP gene expression via mechanism involving p38 MAP kinase activation of transcription factor Elk-1. In cultured neonatal rat atrial myocytes stretch induced BNP gene expression was dependent upon transcription factor Elk-1 binding sites within the BNP gene promoter. In conclusion, hypertrophic signaling in cardiac myocytes involves multiple signaling cascades. Activation of p38 MAPK is required for the development of ET-1 induced hypertrophic phenotype and GATA4 mediated BNP gene expression in cultured ventricular myocytes, and for stretch induced Elk-1 dependent BNP gene expression in atrial myocytes. PKCα is involved in PE induced hypertrophic response and PE induced switch in gene programming inducing expression of α-SkA, the fetal form of cardiac α-actin.

Genetic interactions that underlie developmental processes such as cell differentiation and pattern formation are complex and difficult to elucidate. Neural Crest (NC) cells and their derivatives offer an optimal system in which to probe for these complex interactions as they acquire different cell fates and constitute a variety of structures. The transcription factors Sox10 and Pax3 as well as the transmembrane receptor Endothelin receptor b (Ednrb) are temporally and spatially co-expressed early in NC cells and mutations in these genes lead to similar hypopigmentation phenotypes due to a reduced number of NC-derived melanocyte precursors, the melanoblasts. The goal of this study was to establish whether Sox10 and Ednrb or Pax3 and Ednrb interact to promote normal murine melanocyte development. Crosses of Sox10 or Pax3 with Ednrb heterozygous mutants showed that the double heterozygous hypopigmentation phenotype was significantly more pronounced than phenotypes of single heterozygotes, implying that a synergistic interaction exists between Sox10 and Ednrb and Pax3 and Ednrb. This interaction was further explored by the attempt to rescue the Sox10 and Pax3 hypopigmentation phenotypes by the transgenic addition of Ednrb to melanoblasts. Pigmentation was completely restored in the Sox10 and partially restored in the Pax3 mutant mice. The comparison of the number of melanoblasts in transgenic and non-transgenic Sox10 mutant embryos showed that the transgenic rescue occurred as early as E11.5, a critical time for melanoblast population expansion. Cell survival assays indicated that the rescue was not due to an effect of the transgene on melanoblast survival. A novel phenotype arose when studying the interaction between Ednrb and Pax3. Newborns appeared normal but by 3.5 weeks of age, the affected pups were smaller than normal littermates and developed a dome-shaped head; some also developed thoracic kyphosis. Affected pups were dead by 4 weeks of age: 80% were Pax3Sp/+ and 75% were female. When compared to normal littermates, affected mice had brains with enlarged 4th ventricles and more glia while skeletal staining showed kyphosis, wider rib cages and pelvic differences. An epistatic interaction resulting from the mixing of genetic backgrounds that is exacerbated in the presence of Pax3 heterozygosity is suspected.

Addition of lysophosphatidic acid (LPA) to rat aorta-derived endothelial cells significantly induced preproendothelin-1 (preproET-1) mRNA expression. PreproET-1 mRNA levels reached a plateau within 1 h after the addition of 0.5 μM LPA and declined after 2 h. The induction was superinduced by cycloheximide and was blocked by actinomycin D. Suramin, an LPA receptor antagonist, abolished the induction of preproET-1 mRNA by LPA. Protein kinase C inhibitors, H7 and bisindolylmaleimide, were able to block the induction. Transient transfection experiment revealed that the elevated preproET-1 mRNA was a result of the activation of ET-1 gene activity. Electrophoretic mobility shift assay revealed that LPA stimulated the binding of AP-1. The secreted level of ET-1 was elevated 2.3-fold after 12 h of stimulation with LPA. Our results suggest that the upregulation of preproET-1 by LPA may serve to augment and prolong the vasoconstriction action of LPA.

Thromboxane A2 (TXA2) and ET-1 have been known to play important roles in modulating vascular contraction and growth. The present study was undertaken to examine the effect of TXA2 on the induction of endothelin-1 (ET-1) mRNA and protein levels in smooth muscle cells derived from rat heart. U-46619, a stable TXA2 mimetic, superinduced preproET-1 mRNA in the presence of cycloheximide in these cells. This effect could be blocked by SQ-29548, a TXA2/prostaglandin H2 receptor antagonist and by actinomycin D, an RNA synthesis inhibitor. In addition, H7, a protein kinase C inhibitor, could abolish the induction. Transient transfection experiment revealed that the elevated ET-1 mRNA level after U-46619 treatment was a result of the activation of ET-1 gene activity. The elevated ET-1 message level was accompanied by increased ET-1 release into the cultured medium. These results show that the short-lived TXA2 can induce potent and long-lived ET-1. These findings support a potential role for ET-1 in the pathogenesis of coronary atherosclerosis and hypertension evoked by TXA2.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20275号 / 医博第4234号 / 新制||医||1021(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 横出 正之, 教授 小西 靖彦, 教授 山下 潤 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

Recently, C-reactive protein (CRP) was shown to affect intracellular calcium signaling and blood pressure in vitro and in vivo, respectively. The aim of the present study was to further investigate if a direct effect on G-protein coupled receptor (GPCR) signaling by CRP can be observed by using CRP in combination with different GPCR agonists on spontaneously beating cultured neonatal rat cardiomyocytes. All used agonists (isoprenaline, clenbuterol, phenylephrine, angiotensin II and endothelin 1) affected the beat rate of cardiomyocytes significantly and after washing them out and re-stimulation the cells developed a pronounced desensitization of the corresponding receptors. CRP did not affect the basal beating-rate nor the initial increase/decrease in beat-rate triggered by different agonists. However, CRP co-incubated cells did not exhibit desensitization of the respective GPCRs after the stimulation with the different agonists. This lack of desensitization was independent of the GPCR type, but it was dependent on the CRP concentration. Therefore, CRP interferes with the desensitization of GPCRs and has to be considered as a novel regulator of adrenergic, angiotensin-1 and endothelin receptors.

Heart valve disease is currently one of the leading forms of heart disease. Current literature has shown that endothelin I, angiotension II and 5-HT are vasoactive agents which cause concentration dependent contractions in aortic valve leaflet tissue. This study tested the mechanical properties of leaflets cut in the radial direction after they were exposed to the agents at varied concentrations or for 0.5, 6 or 24 hours. The elastic modulus, ultimate tensile strength and the yield strength were calculated. In the time trials the elastic modulus and the ultimate tensile strength both showed a significant increase at 24-hours. However, there were no significant differences found between the concentrations. Indicating the amount of vasoactive agent is not as significant as the length of exposure.