Cellular models and viral vectors for skeletal and cardiac muscle research

Skeletal and cardiac muscle disorders are associated with substantial morbidity and mortality. Despite many improvements in the medical and surgical management of these disorders, development of effective treatments has proven to be challenging. This is because of the limited suitability of existing experimental models for acquiring a thorough understanding of the mechanisms underlying skeletal and cardiac muscle diseases and the lack of efficiency and specificity of many of the currently available therapeutic interventions. Therefore, the aim of this thesis was to establish and use dedicated cellular models in combination with genetic interventions to study the biology of skeletal and cardiac muscles in healthy and diseased states and thereby identify potential targets for future therapeutic interventions. The experiments described in this thesis indeed emphasized the importance of cellular models for (i) elucidating the mechanisms underlying skeletal and cardiac muscle diseases and (ii) identification of novel therapeutic targets. This thesis also underlined the usefulness of viral vector-mediated gene transfer technology for development of biological assays and the evaluation of therapeutic targets. In conclusion, application of in vitro models in combination with genetic interventions can improve our understanding of skeletal and cardiac muscle diseases and aid development of new therapies for these disorders.UBL - phd migration 201

Generation of Helper Plasmids Encoding Mutant Adeno-associated Virus Type 2 Capsid Proteins with Increased Resistance against Proteasomal Degradation

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The proarrhythmic features of pathological cardiac hypertrophy in neonatal rat ventricular cardiomyocyte cultures

Different factors may trigger arrhythmias in diseased hearts, including fibrosis, cardiomyocyte hypertrophy, hypoxia, and inflammation. This makes it difficult to establish the relative contribution of each of them to the occurrence of arrhythmias. Accordingly, in this study, we used an in vitro model of pathological cardiac hypertrophy (PCH) to investigate its proarrhythmic features and the underlying mechanisms independent of fibrosis or other PCH-related processes. Neonatal rat ventricular cardiomyocyte (nr-vCMC) monolayers were treated with phorbol 12-myristate 13-acetate (PMA) to create an in vitro model of PCH. The electrophysiological properties of PMA-treated and control monolayers were analyzed by optical mapping at day 9 of culture. PMA treatment led to a significant increase in cell size and total protein content. It also caused a reduction in sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 level (32%) and an increase in natriuretic peptide A (42%) and alpha 1-skeletal muscle actin (34%) levels, indicating that the hypertrophic response induced by PMA was, indeed, pathological in nature. PMA-treated monolayers showed increases in action potential duration (APD) and APD dispersion, and a decrease in conduction velocity (CV; APD(30) of 306 +/- 39 vs. 148 +/- 18 ms, APD30 dispersion of 85 +/- 19 vs. 22 +/- 7 and CV of 10 +/- 4 vs. 21 +/- 2 cm/s in controls). Upon local 1-Hz stimulation, 53.6% of the PMA-treated cultures showed focal tachyarrhythmias based on triggered activity (n = 82), while the control group showed 4.3% tachyarrhythmias (n = 70). PMA-treated nr-vCMC cultures may, thus, represent a well-controllable in vitro model for testing new therapeutic interventions targeting specific aspects of hypertrophy-associated arrhythmias.NEW & NOTEWORTHY Phorbol 12-myristate 13-acetate (PMA) treatment of neonatal rat ventricular cardiomyocytes (nr-vCMCs) led to induction of many significant features of pathological cardiac hypertrophy (PCH), including action potential duration prolongation and dispersion, which provided enough time and depolarizing force for formation of early afterdepolarization (EAD)-induced focal tachyarrhythmias. PMA-treated nr-vCMCs represent a well-controllable in vitro model, which mostly resembles to moderate left ventricular hypertrophy (LVH) rather than severe LVH, in which generation of a reentry is the putative mechanism of its arrhythmias.Cardiolog

Cardiomyogenic differentiation of human adipose-derived mesenchymal stem cells transduced with Tbx20-encoding lentiviral vectors

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T-Box20 inhibits osteogenic differentiation in adipose-derived human mesenchymal stem cells: the role of T-Box20 on osteogenesis

Background Skeletal development and its cellular function are regulated by various transcription factors. The T-box (Tbx) family of transcription factors have critical roles in cellular differentiation as well as heart and limbs organogenesis. These factors possess activator and/or repressor domains to modify the expression of target genes. Despite the obvious effects of Tbx20 on heart development, its impact on bone development is still unknown. Methods To investigate the consequence by forced Tbx20 expression in the osteogenic differentiation of human mesenchymal stem cells derived from adipose tissue (Ad-MSCs), these cells were transduced with a bicistronic lentiviral vector encoding Tbx20 and an enhanced green fluorescent protein. Results Tbx20 gene delivery system suppressed the osteogenic differentiation of Ad-MSCs, as indicated by reduction in alkaline phosphatase activity and Alizarin Red S staining. Consistently, reverse transcription-polymerase chain reaction analyses showed that Tbx20 gain-of-function reduced the expression levels of osteoblast marker genes in osteo-inductive Ad-MSCs cultures. Accordingly, Tbx20 negatively affected osteogenesis through modulating expression of key factors involved in this process. Conclusion The present study suggests that Tbx20 could inhibit osteogenic differentiation in adipose-derived human mesenchymal stem cells.Cardiolog

Cardiomyogenic differentiation of human adipose‐derived mesenchymal stem cells transduced with Tbx20

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Overexpression of MicroRNA-148b-3p stimulates osteogenesis of human bone marrow-derived mesenchymal stem cells: the role of MicroRNA-148b-3p in osteogenesis

BackgroundMesenchymal stem cells (MSCs) are attractive choices in regenerative medicine and can be genetically modified to obtain better results in therapeutics. Bone development and metabolism are controlled by various factors including microRNAs (miRs) interference, which are small non-coding endogenous RNAs.MethodsIn the current study, the effects of forced miR-148b expression was evaluated on osteogenic activity. Human bone marrow-derived mesenchymal stem cells (BM-MSCs) were transduced with bicistronic lentiviral vector encoding hsa-miR-148b-3p or -5p and the enhanced green fluorescent protein. Fourteen days post-transduction, immunostaining as well as Western blotting were used to analyze osteogenesis.ResultsOverexpression of miR-148b-3p increased the osteogenic differentiation of human BM-MSCs as demonstrated by anenhancement of mineralized nodular formation and an increase in the levels of osteoblastic differentiation biomarkers, alkaline phosphatase and collagen type I.ConclusionsSince lentivirally overexpressed miR-148b-3p increased osteogenic differentiation capability of BM-MSCs, this miR could be applied as a therapeutic modulator to optimize bone function.Cardiolog

MicroRNA-499a-5p Promotes Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells to Cardiomyocytes

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Development of a Lentivirus Vector-Based Assay for Non-Destructive Monitoring of Cell Fusion Activity

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NFAT3 gene transfer to counteract the pro-arrhythmic electrophysiological changes accompanying pathological cardiac hypertrophy

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