Clinical translation of stem cell therapies for heart disease is limited by a risk of potentially life-threatening ventricular arrhythmias seen following cardiomyocyte delivery in large animal models. Enhancing cardiomyocyte maturation may reduce this arrhythmogenic risk by reducing automaticity of delivered cardiomyocytes. We tested whether human induced pluripotent stem cell (hiPSC)-derived endothelial cells can enhance maturation and suppress automaticity of iPSC-derived cardiomyocytes in vitro. We found that co-culture of hiPSC-derived endothelial cells with hiPSC-derived cardiomyocytes significantly increased protein expression of cardiac troponin T, cardiac troponin I, Kir2.1, connexin 43, and CD36. In addition, using a stretchable mesh nanoelectronics device, we found that hiPSC-derived endothelial cells accelerated electrical maturation of hiPSC-derived cardiomyocytes and progressively suppressed cardiomyocyte automaticity in vitro (Figure). Using single cell RNA-seq, we identified a subpopulation of hiPSC-derived cardiomyocytes that is eliminated upon co-culture with hiPSC-derived endothelial cells. Further work will investigate whether this subpopulation of cardiomyocytes is responsible for automaticity of cardiomyocyte cultures. Figure. Induced pluripotent stem cell (iPSC)-derived cardiomyocytes alone (CM only) or iPSC-derived cardiomyocytes co-cultured with iPSC-derived endothelial cells (CM+EC) were seeded onto a stretchable mesh nanoelectronics device. Unstimulated voltage tracings at day 30 of cardiomyocyte differentiation show cardiomyocytes with a slower beating rate and more narrow action potential when co-cultured with iPSC-derived endothelial cells compared to iPSC-derived cardiomyocytes alone.
Directed differentiation of human pluripotent stem cells (PSC) into cardiomyocytes via manipulation of Wnt signaling leads to generation of immature cardiomyocytes, more closely resembling a fetal state. It has become increasingly apparent that metabolic parameters regulate of cardiomyocyte maturation. The forkhead box (FOX) family of transcription factors has previously been shown to regulate metabolic phenotype in neonatal cardiomyocytes through a balance between FOXO and FOXM proteins. Therefore, we hypothesized that dysregulation of FOXO-FOXM1 signaling inhibits maturation of iPSC-derived cardiomyocytes (iPSC-CMs). We cultured iPSC-CMs in 3D suspension culture using an orbital shaker. iPSC-CMs were treated with RCM-1 (FOXM1 inhibitor), LOM612 (FOXO nuclear translocator), or AS1842856 (FOXO inhibitor) starting 2 days after onset of beating. We found that inhibition of FOXO with AS1842856 resulted in loss of expression of cardiac-specific markers such as cardiac troponin T as well as loss of spontaneous beating. In contrast, inhibition of FOXM1 with RCM-1 or activation of FOXO with LOM612 resulted in retention of a cardiomyocyte phenotype with continued expression of cardiac troponin T but with significantly increased expression membrane protein expression of Kir2.1 (Figure), the protein largely responsible for maintaining the resting membrane potential in cardiomyocytes. These results suggest that inhibition of FOXM1 and/or activation of FOXO signaling may facilitate maturation of iPSC-derived cardiomyocytes. Figure. (A) % of TNNT2+ iPSC-derived cardiomyocytes that express Kir2.1 and (B) Mean fluorescence intensity of Kir2.1 in iPSC-derived cardiomyocytes after treatment with DMSO (vehicle control), RCM-1, LOM612, or AS1842856. *p<0.05, ***p<0.001, ****p<0.0001 by one-way ANOVA with Dunnett’s multiple comparisons test.
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