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Title: Cyclic nucleotide signalling in cardiac myocytes from the mdx model of Duchenne muscular dystrophy
Author: Brescia, Marcella
ISNI:       0000 0004 7229 0924
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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Background and Aims: Duchenne muscular dystrophy (DMD), the most frequent muscular dystrophy, is caused by mutations in the dystrophin gene resulting in the absence of dystrophin. Loss of cardiac dystrophin eventually leads to dilated cardiomyopathy and congestive heart failure in at least 20% of patients. Previous studies have shown that inhibition of enzymes that degrade cGMP improves cardiac contractility, energy metabolism and cardiac myocyte integrity in the DMD mouse model mdx. The aim of this project is to explore whether defective cGMP and cAMP signalling is a feature of mdx cardiac myocytes and whether this may play a role in the pathogenesis of the cardiomyopathy associated with dystrophin deficiency. Methods: Live-cell fluorescent imaging of Fluoresence Resonance Energy Transfer (FRET) has been used to investigate real-time changes in cAMP and cGMP in specific subcellular compartments of neonatal and adult isolated cardiomyocytes. The IonOptix contractility and force transducer system were used to explore the contractile performance and force generation upon contraction in mdx adult cardiomyocytes. Results: cAMP and cGMP regulation and compartmentalisation seem to be significantly altered in mdx mice cardiomyocytes. The data suggest that the activity of several isoforms of phosphodiesterase and the ability to generate cGMP and cAMP in specific subcellular compartments is altered in neonatal cardiomyocytes (NCM) from the mdx model, indicating that not only the cGMP pathway might underpin the cardiomyopathy associated with DMD but disruption of cAMP signalling may also play a role. Analysis of cyclic nucleotide signalling in adult mdx cardiac myocytes indicated significantly higher levels of oxidised sGC and PDE mRNA levels. Additionally, adult mdx cardiomyocytes presented lower nNOS expression in the PM and in the ER. Basal levels of cyclic nucleotides significantly changed with age, suggesting that compensatory mechanisms may develop with age. Furthermore, mdx cardiomyocytes showed significantly impaired force of contraction which was abolished upon IBMX treatment suggesting that altered PDE activity might underpin defects in contractility. Conclusions: In summary, the data presented in this thesis supports the hypothesis that defective cyclic nucleotides signalling might play a role in the cardiomyopathy associated with DMD in the mdx.
Supervisor: Zaccolo, Manuela Sponsor: National Council for Scientific and Technological Development (CNPq)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available