One of the highlights of the recent FCVB meeting was, without a doubt, the Keynote lecture by Prof Joseph Wu, Director of the Stanford Cardiovascular Institute at the Stanford School of Medicine. Prof Wu elegantly condensed an impressive number of ground-breaking studies from his own group, in the context of the fast-moving revolution that we’re witnessing in regenerative medicine. Prof. Wu delivered a talk that was accessible to the non-stem cell expert, yet fascinating to all.
The Wu lab studies the biological mechanisms of adult stem cells, including embryonic stem (ES) cells, and induced pluripotent stem cells (iPSCs), combining next generation sequencing, physiological testing, and molecular imaging technologies to better understand stem cell biology.Starting with the initial discovery of ES cells (their promise and their limitations), Wu described the real explosion in the field came with Shinya Yamanaka’s game changing discovery that human skin fibroblasts could be efficiently induced to form ES-like cells: induced pluripotent stem cells (iPSCs). They, like ES cells, fulfill all the criteria of stemness: clonality, self-renewal and multipotency. With the potential to give rise to all cell types required in the adult comes the prospect of complete regeneration of the human heart. A critical advantage over ES cells is the ability to derive patient-specific iPSCs and thereby overcome the obstacle of immune rejection.After the early waves of excitement, researchers in the cardiovascular field were set back a little with the realization that generating fully functional, mature cardiomyocytes from iPSCs was far from straight-forward. The Wu lab has been at the forefront of the move to refine protocols that augment cardiac differentiation, with chemically defined medium and small molecule inhibitors, yields in excess of 90% are now reproducibly achieved, compared with 5% efficiency only two years ago.Phenotype and functional maturity have also been markedly enhanced but there remains scope for further refinement. While such improvements are essential before iPSC-derived cardiomyocytes (iPSC-CMs) could be considered a viable option for regenerative therapy, they have found great utility in disease modelling, drug discovery and toxicity testing. Wu illustrated these uses with a selection of pertinent examples from his own laboratory. iPSC-CMs have been used successfully to model cardiac conduction and sarcomere defects, including long QT syndrome, tachycardia, dilated and hypertrophic cardiomyopathies.One such example given was that of the MYH7 mutation which underlies familial HCM. The abnormal calcium handling that presents in the patient is recapitulated in their iPSC-CMs, as were cellular enlargement (aggravated in response to isoproterenol) and contractile arrhythmia at the single-cell level. Dysregulated Ca2+ cycling and elevation in intracellular Ca2+ were confirmed as mechanisms for disease pathogenesis. Pharmacological restoration of Ca2+ homeostasis, with calcium channel blockers such as verapamil, was shown to prevent development of hypertrophy and electrophysiological irregularities.Findings from studies such as this will help elucidate the mechanisms underlying the development of cardiomyopthies and identify novel therapies for the disease. Wu described the utility of iPSC-CMs for patient-specific drug screening research, with the recent awareness of disease-specific susceptibility to cardiotoxicity. Cisapride, used to treat severe heartburn and diabetic gastroparesis, was given as a notable example. The drug was withdrawn in 2000, following reports of prolonged QT interval and Torsades de pointes, including many deaths, despite originally proving safe in clinical trials and in the majority of individuals who were routinely prescribed the drug. Screening a library of patient-derived iPSC-CMs confirmed the safety of cisapride in control and DCM patients, but not in LQT and HCM patients. The ability to test drugs on different patient groups, or even an individual patient basis, will provide greater confidence over safety than ever before.It was clear from the talk that rapid progress is being made on so many fronts. Genome editing of isogenic iPSCs means that disease mutations can be modeled without needing to recruit patients that carry the disease; the whole process, from TALEN-mediated gene editing to functional characterization can be completed in as little as 4-5 weeks. Prospects for therapy using ESCs/iPSCs for cardiac regeneration are still some way off but the first trials for macular degeneration, Parkinson’s disease, multiple sclerosis have been planned.Among the various projects under way in the Wu lab, they are investigating ways of overcoming the challenges of tumorigenicity and immunogenicity associated with ES cells such that their transplantation may one day be a feasible therapeutic option to regenerate failing human hearts.
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