Mosqueira, Diogo
(2018)
Disease modeling hypertrophic cardiomyopathy using CRISPR/Cas9 genome editing technology in human pluripotent stem cell-derived cardiomyocytes.
PhD thesis, University of Nottingham.
Abstract
Hypertrophic cardiomyopathy (HCM) is a prevalent genetic cardiovascular disease affecting 1:500 individuals whose cardiac function is deteriorated due to thickening of the left ventricle of the heart, mostly owing to mutations in sarcomeric genes. Modeling HCM in vitro using human pluripotent stem cell-derived cardiomyocytes (hPSC-CM) offers promise to further investigate the disease mechanisms, towards the development of effective drugs.
Herein, nickase CRISPR/Cas9 genome editing technology was harnessed to introduce the R453C pathological mutation in the MYH7 sarcomeric gene, in three healthy hPSC lines. Monoclonal hPSC lines generated displayed the mutation in one or both alleles, as confirmed by PCR-genotyping and Sanger sequencing. A monolayer cardiac differentiation protocol was applied to the generated hPSC lines, resulting in >90% cardiomyocyte purities, and expression of mutant allele(s) of the MYH7 gene was analysed by RT-PCR.
High-content imaging analysis showed that mutant hPSC-CMs displayed higher expression of hypertrophic marker Brain Natriuretic Peptide (BNP), in comparison to isogenic controls. BNP expression was maximised by treatment with hypertrophic inducer Endothelin-1 and rescued by its antagonist Bosentan. Flow cytometry analysis revealed a mild increase in cell volume of mutant cardiomyocytes relative to their wild-type controls.
Functional evaluation of gene-edited lines exposed higher mitochondrial respiration rates relative to the isogenic controls, with the same mitochondrial content, resulting in a trend towards oxidative stress. Further genome engineering to incorporate a calcium indicator in R453C-MYH7 lines enabled confocal line analysis of calcium transients. MYH7-mutant hPSC-CMs exhibited higher frequency of irregular events in comparison to the healthy control, faster calcium kinetics, and higher resting cytosolic calcium concentration.
Integration of hPSC-CMs in Engineered Heart Tissues (EHTs) and subsequent analysis of contractile force showed that mutant lines had a hypo-contractile and negative clinotropic phenotype relative to their isogenic controls. Moreover, R453C-MYH7 hEHTs showed a more pronounced negative force-frequency relationship in comparison with the healthy lines. These phenotypes were not rescued by treatment with cardiac myosin activator Omecamtiv Mecarbil, suggesting that targeting other mechanisms indirectly related with the contractile apparatus may be a preferred route to attenuate the observed pathological changes.
Finally, transcriptomic analysis of gene-edited lines showed up-regulation of genes associated with fetal gene program, hypertrophy, fibrosis, apoptosis and autophagy, indicating potential molecular mechanisms associated with the observed phenotypes and HCM progression.
Overall, hPSC-CMs bearing the R453C-MYH7 mutation exhibit the main molecular and functional hallmarks of HCM, providing a physiologically-relevant platform that enables further dissection of disease mechanisms and promotes pharmacological intervention.
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