Commercial human iPSC-derived ventricular cardiomyocytes have been available from multiple providers for over a decade, with extensive use in research, drug development and toxicology testing due to their appropriate modelling of primary human ventricular cardiomyocytes. Less work has been performed on human iPSC-derived atrial cardiomyocytes despite the clear phenotypic and pharmacological differences between atrial and ventricular cardiomyocytes, rendering the standard ventricular cardiomyocytes a poor model for atrial research. This is of particular concern as atrial fibrillation (AF) is the most common form of arrhythmia worldwide affecting over 33M people and rising, being a co-morbidity with obesity, stroke, dementia and congestive heart failure. Despite the clear clinical need for better AF treatments there are limited therapeutic options with poor success rates and the 1-year mortality rate for patients with AF remains around 25%. Therefore, there is a clear need for better, more human models of AF.
Axol Bioscience Ltd have developed their iPSC-derived atrial cardiomyocytes (ax2518) and have performed extensive validation studies showing differences in key markers, such as MLC2A, ANP and KCNA5 and electrophysiology between their isogenic atrial and ventricular cardiomyocytes (ax2508). There has been less investigation carried out on the contractility differences between the two cell-types which is of particular relevance to AF. Therefore, Axol have partnered with innoVitro GmBH to examine the phenotypic and pharmacological differences in contractility of Axol’s two forms of cardiomyocytes on their FLEXcyte 96 platform.
innoVitro tested the baseline contractility and the effects of isoprenaline, S-Bay K8644 and the atrial-specific 4-AP and Carbachol, at a range of concentrations on both ax2508 and ax2518. Both sets of cardiomyocytes were grown for 6 days, according to Axol’s protocols, on innoVitro’s FLX-96 plates at a range of seeding densities. They displayed markedly different baseline contractility waveforms and contractility parameters on the FLEXcyte 96, consistent with the typical results seen with the corresponding primary atrial and ventricular cardiomyocytes. The FLEXcyte 96 measured multiple contractility parameters allowing the assessment of the effect of each of the tested compounds. Isoprenaline, Carbachol, 4-AP and S-Bay K8644 produced distinctly different effects on ax2508 and ax2518 in terms of waveform shape, beat rate and beat duration. The IKACh agonist Carbachol for example marked effects on the atrial cells; increasing beat duration (500ms to 700ms) and downstroke duration (140%), but only minimal effects on the ventricular cardiomyocytes. In contrast, the b-adrenoceptor agonist isoprenaline produced only a small increase in amplitude (less than 20%) and reduced beat duration (500ms to 350ms) in atrials but caused a marked reduction in amplitude (to less than 5%) and beat duration (800ms to 400ms) with the ventriculars. All compounds and concentrations were tested at n=4 and assessed using the Wilcoxon rank-sum test. This confirmed Axol’s previous comparison work focussed on the two cell-type’s electrophysiology.
Therefore, Axol’s human iPSC-derived Atrial and Ventricular Cardiomyocytes correctly reproduced the different phenotypes and pharmacology of primary cardiomyocyte sub-types as assessed using the FLEXcyte 96 and, as such, provide the starting point to develop more reliable, physiological-relevant models for research on atrial cardiomyocytes and AF.