Im Rahmen dieser Arbeit wurden zwei humane Varianten des von Wang et al., 1999, erstmals beschriebenen muskelspezifischen Proteins Xin (Huhn und Maus) über Sequenzanalyse, Immunofluoreszenzmikroskopie, Transfektionsstudien und biochemischer Analyse näher charakterisiert. <br /> Die Proteine wurden mit human Xin related proteins 1 und 2 – hXirp1 und 2 –bezeichnet. Die Xin-Proteine enthielten bisher unbekannte, sowie spezifische, repetitive Motive, die aus jeweils mindestens 16 Aminosäuren bestanden. Ihre Aminosäuresequenz, mit einer Vielzahl weiterer putativer Motivsequenzen, verwies auf eine potentielle Funktion von hXirp als Adapterprotein in Muskelzellen. Das hier näher untersuchte hXirp1 lokalisierte an den Zell-Matrix-Verbindungen der Muskel-Sehnen-Übergangszone im Skelettmuskel, sowie an den Zell-Zell-Verbindungen der Glanzstreifen im Herzmuskel. Während der Muskelentwicklung zeigte hXirp1 eine sehr frühe Expression, zusammen mit einer prägnanten Lokalisation an den Prämyofibrillen und deren Verankerungsstrukturen, die auf eine Funktion des Proteins in der Myofibrillogenese deuten. Ektopische Expressionen von hXirp1 in einer Vielzahl von Nichtmuskel-Kulturzellen zeigten wiederum eine Lokalisation des Proteins an den Zell-Matrix-Kontakten dieser Zellen. Am Beispiel von hXirp1 und 2 wurde stellvertretend für die Familie der Xin-Proteine gezeigt, daß es sich bei den repetitiven Motiven um neuartige, F-Aktin bindende Sequenzmotive handelte. Die Xin-Proteine können somit als muskelspezifische, aktinbindende, potentielle Adapterproteine bezeichnet werden, denen eine strukturelle und funktionelle Beteiligung an der Verankerung der Myofibrillen im adulten Muskel, wie auch während der Myofibrillogenese zukommt. / The scope of this work was a further characterization of two human variants of the protein Xin which was reported for chicken and mouse in 1999 by Wang et al. Therefor sequence analysis, immunofluorescence microscopy, transfection studies and biochemical approaches were utilized.<br /> The proteins were named human Xin related proteins 1 und 2 – hXirp1 und 2. Xin-proteins possess specific repetitive motives consisting of a minimum of 16 amino acids each. Concerning further putative motive sequences hXirp is a potential adapter protein in the muscle cell. hXirp1 localized within the cell-matrix-contacts of the myotendinous junction in skeletal muscle as well as within the cell-cell-contacts of the intercalated disc in the cardiac muscle. During the development of muscle cells hXirp1 showed early expression as well as concise localization to premyofibrils and their anchorage structures indicating a potential role for this protein in myofibrillogenesis. Ectopic expression of hXirp1 in several non-muscle cells again revealed localization of this protein to cell-matrix contacts. Considering hXirp1 and 2 as an example for all Xin-proteins it was shown that the repetitive motives are new actin binding motives. The data indicated the Xin-proteins as muscle specific, actin binding and potential adapter proteins with implications in structure and function of anchorage of myofibrils in adult muscle and myofibrillogenesis.

The assembly, form, and function of the heart is regulated by complex mechanical signals originating from intrinsic and extrinsic sources, such as the cytoskeleton and the extracellular matrix. During development, mechanical forces influence the self-assembly of highly organized ventricular myocardium. However, mechanical overload induces maladaptive remodeling of tissue structure and eventual failure. Thus, mechanical forces potentiate physiological or pathological remodeling, depending on factors such as frequency and magnitude. We hypothesized that mechanical stimuli in the form of microenvironmental stiffness, cytoskeletal architecture, or cyclic stretch regulate cell-cell junction formation and cytoskeletal remodeling during development and disease. To test this, we engineered cardiac tissues in vitro and quantified structural and functional remodeling over multiple spatial scales in response to diverse mechanical perturbations mimicking development and disease. We first asked if the mechanical microenvironment impacts tissue assembly. To investigate this, we cultured two-cell cardiac µtissues on flexible substrates with tunable stiffness and monitored cell-cell junction formation over time. As myocytes transitioned from isolated cells to interconnected µtissues, focal adhesions disassembled near cell-cell interfaces and mechanical forces were transmitted almost completely through cell-cell junctions. However, µtissues cultured on stiff substrates mimicking fibrotic microenvironments retained focal adhesions near the cell-cell interface, potentially to reinforce the cell-cell junction in response to excessive forces generated by myofibrils in stiff microenvironments. Intercellular electrical conductance between myocytes was measured as a function of connexin 43 immunosignal and the length-to-width ratio of cell pairs. We observed that conductance was correlated to connexin 43 immunosignal and cell pair length-to-width ratio, indicating that tissue architecture can affect electrical coupling. The impact of mechanical overload was also determined by applying chronic cyclic stretch to engineered cardiac tissues. Stretch activated gene expression patterns characteristic of pathological remodeling, including up-regulation of focal adhesion genes, and impacted sarcomere alignment and myocyte shape. Furthermore, chronic cyclic stretch altered intracellular calcium cycling in a manner similar to heart failure and decreased contractile stress generation, suggestive of maladaptive remodeling. In summary, we show that the assembly, form, and function of cardiac tissue is sensitive to a wide range of mechanical cues that emerge during physiological and pathological growth. / Engineering and Applied Sciences

No description available.

Sudden cardiac death is largely attributable to sudden onset ventricular arrhythmias. Alterations in cardiac conduction, particularly the slowing of conduction velocity is one major factor in arrhythmogenesis. By understanding the mechanisms and factors that modulate cardiac conduction velocity, we can assess and perhaps mitigate the risk of arrhythmia in patients for whom slowed conduction is a arrhythmogenic substrate. Cardiac conduction has traditionally been described by cable theory, which predicts an inverse relationship between extracellular resistance and conduction velocity (CV). However, in studies that reduce extracellular resistance by inducing interstitial edema, there are conflicting results, with some labs showing increased CV when edema is induced with one agent, and others showing reduced CV when edema is induced with a different agent. In the first part of this dissertation, we present experimental data in support of ephaptic coupling (EpC), a theorized mechanism of conduction that resolves these apparent contradictions. In the later part of this dissertation, we address how changes in sodium concentration can alter conduction, despite conventional wisdom suggesting that it should not. We show that when sodium channels are impaired, such as by genetic mutation or pharmacologic blockade, that conduction is sensitized to changes in sodium concentrations that would not otherwise induce changes in CV. We go on to explore the mechanisms that modulate this sensitivity and present data that show it is a function of both EpC and outward potassium currents. Taken together, these data expand our understanding of the mechanics behind cardiac conduction and demonstrate that EpC has a clinically relevant impact on conduction and represents a new pathway to explore in regard to the treatment and management of arrhythmogenic and conduction disorders. / Doctor of Philosophy / In all large animals, life is sustained by the regular coordinated beating of the heart to pump blood throughout the body. Throughout this continuous activity, and even with minute-to-minute changes in heart rate, this electrically driven activity continues without major disruption. Until it doesn't. Major arrhythmias can occur suddenly, and without warning. Over the last century, we have begun to understand some of the reasons why heart, even an injured one, will work normally for hundreds of thousands of beats, and on the next fall into a life-threatening new pattern, and one of the most important of these reasons is the speed of conduction: the spread of electrical activation throughout the heart tissue. Understanding the mechanisms of conduction provides a way to assess and mitigate the risk of arrhythmias and may open up new avenues for treatment and prevention. This dissertation presents evidence for a previously theoretical mechanism of conduction called ephaptic coupling. We show that this electric field mediated form of conduction can be modulated with clinically used osmotic agents, and that it has a physiologically relevant impact on conduction. We also show that hyponatremia (i.e. low sodium), a condition that is traditionally thought to have minimal impact on cardiac conduction, because a significant modulator of conduction when sodium channel functions are impaired. As a great many drugs block sodium channels, this sensitization to hyponatremia and the factors that mediate it are underappreciated concerns that are relevant to a wide array of patients. The new findings presented in this dissertation advance our collective understanding of the mechanisms of cardiac conduction and provide evidence for new avenues of exploration in the prevention and management of arrhythmias and conduction disorders.

No description available.

A sépsis e o choque séptico representam uma síndrome complexa de intensa resposta inflamatória sistêmica, com múltiplas anormalidades fisiológicas e imunológicas, comumente causadas por infecção bacteriana. A principal conseqüência dessa resposta é o comprometimento de muitos órgãos e tecidos. A disfunção cardíaca, decorrente de um prejuízo na contratilidade miocárdica, tem sido reconhecida como um fator importante que contribui para os altos índices de mortalidade observados na sépsis. Dados recentes do nosso laboratório indicam que alterações estruturais no miocárdio podem ser responsáveis pela disfunção cardíaca observada na sépsis. Considerando que a maquinaria contrátil interna das miofibras deve permanecer intimamente conectada com a membrana e a matriz extracelular, o presente estudo foi proposto para avaliar alterações nas comunicações intercelulares e acoplagem mecânica entre os cardiomiócitos vizinhos e avaliar a expressão de proteínas do arcabouço celular e da matriz extracelular (especificamente a laminina-?2) durante a sépsis grave. Nossos resultados mostraram que há uma diminuição na expressão das proteínas envolvidas na formação das gap junctions (conexina43) e junções aderentes (N-caderina), o que resultaria na perda da integridade estrutural dos discos intercalares, alterando o acoplamento mecânico e eletro-químico entre os cardiomiócitos vizinhos. Além disso, demonstramos que há redução na expressão de distrofina e das proteínas que constituem o complexo de glicoproteínas associadas a distrofina (CGD) durante a sépsis experimental. A redução ou perda da expressão de distrofina é o evento primário que ocorre seguido pela degeneração miofilamentar, caracterizada pela lise dos filamentos de actina e miosina. A diminuição na expressão das glicoproteínas associadas à distrofina: -distroglicana e laminina foram considerados eventos secundários. Os resultados sugerem que durante a sépsis induzida por ligação e perfuração do ceco (CLP), há perda de proteínas importantes envolvidas tanto no remodelamento do disco intercalar quanto na expressão de glicoproteínas envolvidas na ligação mecânica entre o citoesqueleto intracelular e a matriz extracelular. Embora estudos funcionais sejam necessários para determinar o efeito direto dessas alterações sobre o miocárdio podemos sugerir que as alterações estruturais são parcialmente responsáveis pela depressão miocárdica observada na sépsis. / Sepsis and septic shock represent a complex syndrome of systemic inflammatory response, with multiple physiological and immunological abnormalities, commonly caused by bacterial infection. The most important consequence of the response is the involvement of many organs and tissues. Cardiac dysfunction, caused by impairment in myocardial contractility, has been recognized as an important factor that contributes to the high mortality observed in sepsis. Evidence from our laboratory indicates that myocardial structural changes could be responsible for sepsis-induced myocardial dysfunction. Taking into account that the contractile machinery inside the myofibers must remain intimately connected with the membrane and extracellular matrix, the present investigation sought to evaluate changes in intercellular communications and mechanical coupling between the neighbor cardiomyocytes and the expression of the cell scaffold protein and extracellular matrix (specifically merosin laminin-2 chain) during the severe sepsis. Our results showed a decrease in the expression of proteins involved in formation of gap junctions (connexin-43) and adherens junctions (N-cadherin). These alterations may result in the loss of intercalated disc structural integrity, changing the mechanical and electrical-chemical coupling between neighboring cardiomyocytes. Additionally, we demonstrated the decrease of dystrophin and dystrophin-glycoprotein complex (DGC) components resulting from severe septic injury. The reduction or loss of dystrophin is the primary event that occurs followed by miofilamentar degeneration characterized by actin and myosin lysis. The decrease of glycoproteins associated with dystrophin: -dystroglican and laminin were considered secondary events. The results suggest that during experimental severe sepsis induced by cecal ligation and puncture (CLP), there is loss of important proteins involved in both the remodeling of the intercalated disc and the glycoproteins expression implicated in the mechanical link between the intracellular cytoskeleton and extracellular matrix. Although the functional studies are needed to determine the direct effect of these alterations on myocardium, we can suggest that myocardial structural changes may be partly responsible for sepsis-induced cardiac depression.

A sépsis e o choque séptico representam uma síndrome complexa de intensa resposta inflamatória sistêmica, com múltiplas anormalidades fisiológicas e imunológicas, comumente causadas por infecção bacteriana. A principal conseqüência dessa resposta é o comprometimento de muitos órgãos e tecidos. A disfunção cardíaca, decorrente de um prejuízo na contratilidade miocárdica, tem sido reconhecida como um fator importante que contribui para os altos índices de mortalidade observados na sépsis. Dados recentes do nosso laboratório indicam que alterações estruturais no miocárdio podem ser responsáveis pela disfunção cardíaca observada na sépsis. Considerando que a maquinaria contrátil interna das miofibras deve permanecer intimamente conectada com a membrana e a matriz extracelular, o presente estudo foi proposto para avaliar alterações nas comunicações intercelulares e acoplagem mecânica entre os cardiomiócitos vizinhos e avaliar a expressão de proteínas do arcabouço celular e da matriz extracelular (especificamente a laminina-?2) durante a sépsis grave. Nossos resultados mostraram que há uma diminuição na expressão das proteínas envolvidas na formação das gap junctions (conexina43) e junções aderentes (N-caderina), o que resultaria na perda da integridade estrutural dos discos intercalares, alterando o acoplamento mecânico e eletro-químico entre os cardiomiócitos vizinhos. Além disso, demonstramos que há redução na expressão de distrofina e das proteínas que constituem o complexo de glicoproteínas associadas a distrofina (CGD) durante a sépsis experimental. A redução ou perda da expressão de distrofina é o evento primário que ocorre seguido pela degeneração miofilamentar, caracterizada pela lise dos filamentos de actina e miosina. A diminuição na expressão das glicoproteínas associadas à distrofina: -distroglicana e laminina foram considerados eventos secundários. Os resultados sugerem que durante a sépsis induzida por ligação e perfuração do ceco (CLP), há perda de proteínas importantes envolvidas tanto no remodelamento do disco intercalar quanto na expressão de glicoproteínas envolvidas na ligação mecânica entre o citoesqueleto intracelular e a matriz extracelular. Embora estudos funcionais sejam necessários para determinar o efeito direto dessas alterações sobre o miocárdio podemos sugerir que as alterações estruturais são parcialmente responsáveis pela depressão miocárdica observada na sépsis. / Sepsis and septic shock represent a complex syndrome of systemic inflammatory response, with multiple physiological and immunological abnormalities, commonly caused by bacterial infection. The most important consequence of the response is the involvement of many organs and tissues. Cardiac dysfunction, caused by impairment in myocardial contractility, has been recognized as an important factor that contributes to the high mortality observed in sepsis. Evidence from our laboratory indicates that myocardial structural changes could be responsible for sepsis-induced myocardial dysfunction. Taking into account that the contractile machinery inside the myofibers must remain intimately connected with the membrane and extracellular matrix, the present investigation sought to evaluate changes in intercellular communications and mechanical coupling between the neighbor cardiomyocytes and the expression of the cell scaffold protein and extracellular matrix (specifically merosin laminin-2 chain) during the severe sepsis. Our results showed a decrease in the expression of proteins involved in formation of gap junctions (connexin-43) and adherens junctions (N-cadherin). These alterations may result in the loss of intercalated disc structural integrity, changing the mechanical and electrical-chemical coupling between neighboring cardiomyocytes. Additionally, we demonstrated the decrease of dystrophin and dystrophin-glycoprotein complex (DGC) components resulting from severe septic injury. The reduction or loss of dystrophin is the primary event that occurs followed by miofilamentar degeneration characterized by actin and myosin lysis. The decrease of glycoproteins associated with dystrophin: -dystroglican and laminin were considered secondary events. The results suggest that during experimental severe sepsis induced by cecal ligation and puncture (CLP), there is loss of important proteins involved in both the remodeling of the intercalated disc and the glycoproteins expression implicated in the mechanical link between the intracellular cytoskeleton and extracellular matrix. Although the functional studies are needed to determine the direct effect of these alterations on myocardium, we can suggest that myocardial structural changes may be partly responsible for sepsis-induced cardiac depression.

No description available.