Date Published: July 25, 2019
Publisher: Public Library of Science
Author(s): Peter R. T. Bowman, Godfrey L. Smith, Gwyn W. Gould, Makoto Kanzaki.
Induced pluripotent stem cell derived cardiomyocytes (iPSC-CM) have the potential to transform regenerative cardiac medicine and the modelling of cardiac disease. This is of particular importance in the context of diabetic cardiomyopathy where diabetic individuals exhibit reduced cardiac diastolic contractile performance in the absence of vascular disease, significantly contributing towards high cardiovascular morbidity. In this study, the capacity of iPSC-CM to act as a novel cellular model of cardiomyocytes was assessed. The diabetic phenotype is characterised by insulin resistance, therefore there was a specific focus upon metabolic parameters. Despite expressing crucial insulin signalling intermediates and relevant trafficking proteins, it was identified that iPSC-CM do not exhibit insulin-stimulated glucose uptake. iPSC-CM are spontaneously contractile however contraction mediated uptake was not found to mask any insulin response. The fundamental limitation identified in these cells was a critical lack of expression of the insulin sensitive glucose transporter GLUT4. Using comparative immunoblot analysis and the GLUT-selective inhibitor BAY-876 to quantify expression of these transporters, we show that iPSC-CM express high levels of GLUT1 and low levels of GLUT4 compared to primary cardiomyocytes and cultured adipocytes. Interventions to overcome this limitation were unsuccessful. We suggest that the utility of iPSC-CMs to study cardiac metabolic disorders may be limited by their apparent foetal-like phenotype.
Diabetes is one of the leading healthcare challenges worldwide. Whilst the most common major complication of this condition is vascular disease and therefore increased incidence of stroke or myocardial infarction, there is also a significantly elevated direct risk of heart failure . This is due in part to an impairment of diastolic cardiac contractile function in diabetic individuals independent of vascular disease termed diabetic cardiomyopathy (DCM) [2–4]. Given the high rate of cardiovascular mortality associated with diabetes combined with the lack of DCM specific treatments available, improved understanding of the pathophysiological mechanisms underlying this condition is of clinical relevance.
The overarching aim of this study was to assess the potential of iPSC-CM to act as the basis of a novel cellular model of DCM. Primarily, in order to be considered viable candidates, iPSC-CM must exhibit a reproducible and robust insulin-stimulated glucose uptake response. Initial data suggested that this may be possible, based upon the observation that iPSC-CM express and can activate molecules such as Akt and ERK1/2, indicating that key insulin signalling machinery to intermediates involved in stimulating glucose transport are intact. However, we were unable to demonstrate insulin-stimulated glucose transport in iPSC-CMs. A central feature of diabetic physiology is insulin resistance in glucose metabolism. As these cells do not exhibit an insulin response, their utility as a model for DCM must be viewed with caution . This conclusion was reached using cells obtained from 2 separate commercial sources, suggesting that this is not likely to be a limitation unique to iPSC-CM generated from one specific manufacturer.
Overall, we suggest that iPSC-CM are not suitable for use as the basis of a novel cellular model of DCM, due to their lack of insulin stimulated glucose uptake response. This appears to be primarily the result of an immature metabolic phenotype, characterised by a lack of protein expression of the insulin sensitive GLUT4 transporter. Initial attempts to increase iPSC-CM GLUT4 expression were unsuccessful. Development of methods to enhance GLUT4 expression might help realise the significant potential of iPSC-CMs.