Browsing by Subject "Heart"
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item CAMTA: A Signal-Responsive Transcription Factor That Promotes Cardiac Growth by Opposing Class II Histone Deacetylases(2007-05-23) Song, Kunhua; Olson, Eric N.Cardiac growth is finely regulated by transcriptional circuits. In an effort to discover new regulators of cardiac growth, I performed a eukaryotic expression screen for activators of the atrial natriuretic factor (ANF) gene, a cardiac-specific marker of hypertrophic signaling and embryonic development. I discovered that a family of transcription factors, called CAMTAs, regulate the ANF promoter. CAMTA proteins were first discovered in plants, however, little was known of the mechanism of their action and biological function and virtually nothing was known about mammalian CAMTA proteins, CAMTA1 and CAMTA2. CAMTA1 and CAMTA2 are enriched in embryonic and adult hearts, skeletal muscle at the embryonic stage, and brain. To define the mechanism whereby CAMTA2 activates the ANF promoter, I used a series of promoter deletion mutants to map the cis-regulatory sequences that confer responsiveness to CAMTA2. I found that CAMTA activates the ANF gene, at least in part, by associating with Nkx2-5, a cardiac transcription factor. CAMTA proteins also activate promoters of myogenin and beta myosin heavy chain via direct DNA binding. Therefore, CAMTAs activate target genes through diverse mechanisms. Over-expression of CAMTA2 in vitro and in vivo promotes cardiac growth. Based on the ability of CAMTA2 to induce hypertrophy, I tested whether signaling molecules implicated in cardiac hypertrophy might enhance the activity of CAMTA2. I discovered that the transcriptional activity of CAMTAs is governed by association with class II histone deacetylases (HDACs), which negatively regulate cardiac growth. Mice homozygous for a mutation in the CAMTA2 gene are defective in cardiac growth in response to pressure overload and neurohumoral signaling, whereas mice lacking HDAC5, a class II HDAC are sensitized to the pro-hypertrophic actions of CAMTA. CAMTA proteins are also required for embryonic heart development, as demonstrated by heart defects in mice with low dosage of CAMTA1. These findings reveal a transcriptional regulatory mechanism that modulates cardiac growth and gene expression by linking cardiac growth signals to the cardiac genome.Item Control of Cardiac and Limb Development by the bHLH Transcription Factors DHAND and eHAND(2004-05-04) McFadden, David Glenn; Srivastava, DeepakMembers of the basic helix-loop-helix (bHLH) transcription factor family regulate the specification and differentiation of multiple cell lineages during embryonic development. The bHLH proteins dHAND and eHAND are expressed in complimentary and overlapping patterns during embryogenesis, and gene knockout studies have demonstrated that dHAND and eHAND null embryos die from defects in right ventricular and placental development, respectively. Therefore, we have investigated three aspects of HAND gene biology. Firstly, in order to determine the mechanisms that establish chamber identity during cardiac development, we have identified a transcriptional enhancer that controls dHAND expression in the embryonic right ventricle, and demonstrated that activity of this element depends on paired binding sites for the GATA family of zinc-finger transcription factors. Secondly, we have generated floxed alleles of murine eHAND in order to investigate the role of eHAND during heart formation. These studies have identified a novel role for eHAND during cardiac valve formation, and demonstrated genetic redundancy of HAND genes during mammalian cardiac morhpogenesis. Finally, we have utilized tissue culture assays and transgenic mice to investigate the mechanisms by which dHAND regulates transcription of downstream target genes. These results suggest that dHAND and eHAND may regulate gene expression independently of direct DNA binding and transcriptional activation.Item Design and implementation of a low-power implantable cardiac monitoring device(2010-12) Shuhatovich, Lev Michael; Valvano, Jonathan W., 1953-; Pearce, John A.The conductance catheter technique is commonly used in research to assess cardiac hemodynamics through measurement of ventricular pressure and volume. In order to perform chronic cardiac studies in murine rodents, a small low-power device capable of performing these measurements is necessary. This thesis presents the design, implementation, and test of such a device, coupled with a radio that allows for the telemetry to be transmitted to a base station. Multiple low-power design techniques were employed in this device, which is surgically embedded in the animal. The total mass of the device with battery is 4 grams, and the device volume is 10cm3. Results show that it is capable of periodic monitoring of pressure volume loops for up to 60 days on a single charge.Item Developing a Model Three-Dimensional Animation of Embryonic Heart Development(2005-05-04) Carre, Ryan; Calver, LewisThree-dimensional animations are often effective in explaining complex phenomena, but altering the finished productions can be cumbersome and costly. The goal of this thesis was to develop a technique for easily altering 3D animations using 2D methods. In conjunction with the Olson Laboratory at the University of Texas Southwestern Medical Center, I created two animations dealing with heart development, based on one 3D animation model. The animations focused on cardiac morphogenesis and transcription factor expression. The purpose of this project was to not only visually communicate cardiac morphogenesis and the expression patterns of transcription factors, but to create a 3D model that can be used as a template for any further visualization of heart development research.Item Development of a bioreactor imaging system for characterizing embryonic stem cell-derived cardiomyocytes(2010-05) Abilez, Oscar John; Suggs, Laura J.; Roy, KrishnenduCardiovascular disease (CVD) affects more than 70 million Americans and is the number one cause of mortality in the United States. Because the regenerative capacity of adult tissues such as the heart is limited, human embryonic stem cells (hESC) have emerged as a source for potential cardiac therapies. However, despite the use of a variety of biochemical differentiation protocols, current yields of hESC-derived cardiomyocytes (CM) have been low. In the case of hESC-CM, which are inherently electromechanically active, additional forms of inducing a mature cardiac fate have not been fully explored. In order to non-invasively visualize and quantify biochemical, electrical, and mechanical stimulation on hESC-CM differentiation in future studies, a bioreactor imaging system has been developed and is described in this report.Item Effect of diabetes on composition and metabolism of heart lipids(Texas Tech University, 1980-08) Paulson, Dennis JNot availableItem Examination of tissue interaction in the developing heart(Texas Tech University, 1983-08) Runyan, Raymond BruceNot availableItem Genetic Dissection of Heart Development in the Fruit Fly Drosophila Melanogaster(2007-12-18) Yi, Peng; Olson, Eric N.The early morphogenetic mechanisms involved in heart formation are evolutionarily conserved. The Drosophila heart, known as the dorsal vessel, functions as a pulsatile tube-like organ containing an inner layer of contractile cardial cells that adhere tightly to an adjacent layer of pericardial cells. A genetic screen for genes that control Drosophila heart development revealed a cardiac defect in which pericardial and cardial cells dissociate causing loss of cardiac function and embryonic lethality. This phenotype resulted from mutations in the genes encoding HMG-CoA Reductase, downstream enzymes in the mevalonate pathway, and G-protein Ggamma 1, which is geranylgeranylated, thus representing an endpoint of isoprenoid biosynthesis. These findings reveal a cardial cell-autonomous requirement of Ggamma 1 geranylgeranylation for heart formation and suggest the involvement of the mevalonate pathway in congenital heart disease. In addition, we found that the heterotrimeric G proteins Gbeta 13F and G-oalpha 47A together with the RGS (regulator of G protein signaling) protein Loco function in the same pathway as Ggamma 1 to regulate septate junction formation in cardial cells of the Drosophila heart. We also present evidence that the septate junction protein Sinuous interacts with Pericardin, a matrix protein secreted by pericardial cells, providing the molecular basis for cardial-pericardial cell adhesion and serving as a mediator of the actions of the mevalonate pathway and heterotrimeric G protein signaling in Drosophila heart development.Item Heart Regeneration: An Evolutionary Tale(2013-01-17) Mahmoud, Ahmed Ibrahim; Sadek,Hesham A., M.D., Ph.D.Lower vertebrates like urodele amphibians and teleost fish retain a robust cardiac regenerative capacity throughout their life, a phenomenon that is mediated through the proliferation of pre-existing cardiomyocytes. The adult mammalian heart lacks any meaningful endogenous regenerative response following injury. However, embryonic mammalian cardiomyocytes are proliferative and exit the cell cycle shortly after birth. The question of whether the mammalian heart lacks this regenerative potential or is lost early after birth was not clear. We were able to show that the hearts of 1-day-old mice regenerated following partial surgical resection of the neonatal heart, a phenomenon that is lost within a week after birth. Thus, for a brief period after birth, the mammalian heart appears to have the capacity to regenerate due to the proliferative competency of cardiomyocytes. However, one major unresolved question was whether the neonatal mouse heart could also regenerate in response to myocardial ischemia, the most common antecedent of heart failure in humans. To examine this question, we induced myocardial infarction (MI) in 1-day-old mice by ligating the left anterior descending coronary artery, and found that this results in extensive myocardial necrosis and systolic dysfunction. Remarkably, the neonatal mouse heart mounted a robust regenerative response, through proliferation of pre-existing cardiomyocytes, which resulted in full functional recovery within 21 days. Moreover, we were able to demonstrate that the neonatal heart is capable of regeneration following mild, but not severe cryoinjury. Therefore, our work identifies a short period of time after birth where the mammalian heart is capable of regeneration following various types of injury. To unravel the molecular mechanisms that regulate the regenerative capacity of the neonatal mammalian heart, we determined that the miR-15 family regulates neonatal heart regeneration through inducing post-natal cardiomyocyte cell cycle arrest. Moreover, inhibition of the miR-15 family at an early post-natal age until adulthood induces cardiomyocyte proliferation in the adult heart and improves left ventricular systolic function following MI. In conclusion, our findings indicate that the mammalian heart harbors a robust regenerative capacity for a short period of time after birth, mediated by proliferation of pre-existing cardiomyocytes, and that the miR-15 family is an important regulator of post-natal cardiomyocytes cell cycle arrest.Item Localization and functional interactions of fibronectin and associated basement membrane proteins during embryonic heart development(Texas Tech University, 1984-08) Kitten, Gregory TThe early embryonic heart is composed of two, cylindrical epithelial layers, an inner endothelium and an outer myocardium. The cardiac jelly (CJ), an a cellular accumulation of extra cellular matrix (ECM), fills the space between the two layers. All cardiac endothelial cells (EC) do not follow an identical course of differentiation. Some of the EC of the atrio ventricular (AV) and outflow tract (OT) regions undergo an epithelial-mesenchymal transition to form mobile cardiac mesenchymal (CM) cells while in other regions (e.g., ventricle), EC differentiate along the lines of a typical vascular endothelium. The mechanisms controlling the biphasic differentiation of EC and the subsequent migration of CM cells are poorly understood. Although the CJ lies between two epithelia and is spatially equivalent to a basement membrane (BM), it has not traditionally been considered to be organized into a BM-like structure. The potential significance of this observation lies in the possibility that BM, or their individual components (i.e., fibronectin (FN), laminin (LH), type IV collagen, and heparan sulfate proteoglycan (HSPG)), may function as the regulatory site o f " epithelial differentiation and morphogenesis. The temporal changes in the localization and the functional involvement of the BM components FN, LM, type IV collagen, and HSPG were investigated with respect to (1) EC attachment and differentiation and (2) CM cell attachment and migration. A cryofixation technique was developed in order to determine the in situ immunohistochemical distribution of the BM components in the CJ. Results indicated that the CJ exists IJS the fusion between a larger, myocardially derived BM and an attenuated, endothelial associated BM. Except for FN, the individual BM components were not all present during early stages. Instead, they appeared in a sequential manner, suggesting that all components of an adult-type B'A are not required to initiate the assembly of a structural and functional BM during development. In the AV and OT, FN lippeared as a progressively expanding gradient of material with the greatest density nearer the myocardium. An in vitro collagen gel bioassay was employed to directly test whether FN or other BM components play a role in EC and CM cell attachment, differentiation, and migration. Biochemical analysis and results from experiments using probes directed against the BH components indicated that mora than one mechanism of attachment, involving FN and/or HSPG, exist during EC development and CM cell migration.Item Regulation Of Exercise-Dependent Cardiac Growth By Micrornas(2013-01-16) Johnson, Brett A.; Olson, Eric N., Ph.D.The heart is an adaptive organ which undergoes pathological or physiological remodeling in response to a variety of stimuli to meet the demands of the body. Chronic exercise training promotes a physiological remodeling response in which the heart increases in size to match loading demands. In this thesis, I present my studies on the function of microRNAs during exercise-induced cardiac remodeling. First, I show the expression of muscle-specific microRNA (miRNA), miR-499, is down-regulated by voluntary free-wheel running in hearts of mice. I hypothesized the reduction of miR-499 may be required for exercise-induced cardiac hypertrophy. I found forced cardiac over-expression of miR-499 was associated with diminished physiological cardiac growth, whereas genetic deletion and antimiR mediated inhibition of miR-499 caused enhanced physiological growth following exercise. I also explored the mechanism by which miR-499 represses exercise-induced cardiac growth. I determined the repressive effects of miR-499 are mediated through regulation of IGF-1/PI-3K/Akt and beta-catenin signaling pathways, which drive physiological growth of the heart. I demonstrated the effects of miR-499 on physiological cardiac growth are mediated, at least in part, through repression of a network of genes including p85-alpha, Rictor, Lin7c and Fzd4. Collectively, the results of my thesis research identify miR-499 as a pivotal regulator of exercise-induced cardiac hypertrophy.Item Theoretical analysis of the regulation of calcium content in the rat cardiac myocyte(Texas Tech University, 2000-12) Gaur, NamitIn mammalian heart, the processes of excitation-contraction (E-C) coupling and Ca-induced Ca release (CICR) depend on the amount of Ca stored in the sarcoplasmic reticulum (SR). Thus the mechanisms controlling the SR Ca load are of importance for our understanding of cardiac performance. It is proposed that the SR Ca release channels activated by luminal Ca provide an adjustable Ca leak pathway, through which the SR can self-regulate its load and maintain stable CICR. It is also proposed that the diastolic fluxes (i.e. Ca fluxes circulating between the sarcoplasmic reticulum and the cytosol in the interval between heart beats) play an important role in Ca regulation. It follows from this proposal that leak from the SR, not uptake into the SR, controls the SR load. With the help of the permeabilized myocyte model, we simulated the effects of changes in SR calcium content on the SR release, both with and without the luminal sensor mechanism during pharmacological interventions of thapsigargin. phosphorylation of phospholamban, tetracaine and caffeine. We then simulated the effects of diastolic fluxes and the luminal sensor mechanism during the tetracaine intervention on the Ca content using a whole-cell Ca dynamics model. Finally, the dominant SR regulatory mechanisms were investigated by carrying out parametric analysis using the permeabilized and the whole-cell myocyte model. Results indicate that the luminal sensor mechanism and the diastolic fluxes accelerate the dynamics of self-regulation during intervention. The presence of the luminal sensor mechanism functions to resist excursions in SR load. Therefore the luminal sensor would be an advantageous control element from a teleological standpoint by providing additional stability to SR Ca dynamics. The flux mechanisms (sarcolemmal pump, forward SR pump, and leak) play dominant roles in SR regulation whereas the contribution due to the reverse pump mode of the SR CaATPase is negligible. These findings have implications for the treatment of cardiac diseases by suggesting potential protein targets for pharmacotherapies and gene therapies.Item Transcriptional and Translational Regulation of Cardiac Progenitors in the Mouse and Zebrafish(2009-01-09) Cordes, Kimberly Rene; Srivastava, DeepakIn vertebrates, the heart is the first organ to function and cardiac progenitors are among the first cell lineages to be established. Transcriptional networks control the specification of cardiac progenitors, however, it is not fully understood how some transcription factors function in particular cardiac progenitor populations. The basic helix-loop-helix, bHLH, transcription factor, Hand2 has been discovered over a decade ago, and has a severe loss-of-function cardiac phenotype in vivo, yet its function is still not completely known. It is expressed in the early cardiac progenitors of the neural crest cells and second heart field lineages. The first part of my thesis touches on the beginnings to understand the role of Hand2 in the cardiac neural crest progenitors. Generally, expression levels in vertebrates reflect the combined transcription of both alleles of the gene being transcribed. Although there are notable exceptions (i.e., X chromosome genes), the presence of only one functional copy or more than two copies of a gene can have detrimental effects on the development of the organism. Many of the genetic examples of congenital heart disease, which affects 1% of live births, are a result of a haploinsufficient gene dose. Like Hand2, which acts in a dosage-sensitive manner to regulate ventricular formation, the precise dose of proteins can be very important in regulating cardiac development. One way to fine-tune the activity of genes is through the newly identified class of small RNAs, microRNAs (miRNAs), which translationally repress the production of proteins by binding to target sites on messenger RNA (mRNA). miRNAs provide a sophisticated way to adjust protein levels in a spatiotemporal manner. One miRNA may control several mRNAs, including transcription factors, which are the 'master switches' that regulate gene expression. And cooperatively, cell type-specific transcription factors can regulate the tissue-specificity of miRNA expression. Together with transcription factors, miRNAs function in cell fate determination, cell differentiation, proliferation and disease progression. Similar to transcription factors, which activate or repress a set of genes in a particular cell type, miRNAs create an environment, tailored for each cell type, allowing translation of some genes to occur, while repressing others. To date, less than a handful of miRNAs have been identified that function during heart development. The latter half of my thesis represents efforts to identify cardiac progenitor miRNAs and understand their function during development. I found that miRNA function is important in the cardiac mesodermal progenitors. In addition, I present a family of miRNAs, miR-143 and miR-145, that is specific to cardiac and smooth muscle progenitors, and I discuss their function in regulating their respective environments during cardiovascular development and disease.Item Transcriptional Regulation of Neural Crest-derived Pharyngeal Arch Artery Development(2004-12-15) Ivey, Kathryn Nicole; Mendelson, Carole R.The heart is the first organ to form and is required for growth and development of mammalian embryos. As the heart matures, formation of the outflow tract is vital to establish appropriate connections with the vasculature. This process requires contribution from specialized neural crest cells, which originate in the neural folds and migrate to give rise to specific segments of the great vessels as well as particular facial structures. Many syndromic birth defects in humans affecting the heart and face arise as a result of inappropriate development of neural crest cells and can be modeled in animals through ablation of premigratory neural crest cells or targeted deletion of genes required for their proliferation, migration or survival. However, the transcription factors and signaling molecules that specify unique subsets of neural crest cells are still being detailed. This thesis represents efforts to understand those particulars. Endothelin-1 (Et-1), a small signaling peptide, is important for development of neural crest-derived structures and targeted deletion of the gene encoding Et-1 or its receptor, Endothelin-A (EtA), results in craniofacial and outflow tract anomalies along with downregulation of particular neural crest-derived pharyngeal arch mesenchyme markers. Mice deficient for both Gaq and Ga 11 are phenotypically similar to EtA or Et-1-null mice. My analysis of expression patterns of Et-1 dependent and independent transcription factors in Gaq /G a11-deficient embryos revealed that expression of genes encoding Et-1 dependent transcription factors was specifically downregulated in the pharyngeal arches of Gaq /G a11-deficient mice indicating that Gaq and Ga11 proteins serve as intracellular mediators of Et-1 signaling in the pharyngeal arch mesenchyme. Et-1 is also important for development of the neural crest-derived fetal vessel, the ductus arteriosus, which bridges the pulmonary and systemic circulations during gestation and must close at birth for extrauterine survival. The ductus arteriosus is composed of highly differentiated, contractile smooth muscle. I found that Et-1 is expressed specifically in the smooth muscle of the ductus arteriosus during development along with Hif2a and Ap2ᠡnd that, through epistatic relationships and negative feedback regulation, these three factors cooperatively regulate development of the specialized, neural crest-derived smooth muscle of this vessel.