Thorac Cardiovasc Surg 2014; 62 - SC184
DOI: 10.1055/s-0034-1367445

Cardiomyocyte derived from induced pluripotent stem cells are more sensitive to ischemia then naïve cardiomyocytes

A. Brodarac 1, B. Oberwallner 1, T. Saric 2, Y.-H. Choi 3, J. Hescheler 2, C. Stamm 4
  • 1Berlin Center for Regenerative Therapies, Berlin, Germany
  • 2Universität zu Köln, Neurophysiologie, Köln, Germany
  • 3Universität zu Köln, Herzchirurgie, Köln, Germany
  • 4Deutsches Herzzentrum Berlin, Herz-, Thorax- und Gefäßchirurgie, Berlin, Germany

Objectives: Cardiomyocytes derived from induced pluripotent stem cells (iPS-CM) may be suitable for myocardial repair. While their phenotype and function in standard culture conditions is comparable to that of naïve cardiomyocytes, the iPS-CM response to ischemia has so far not been investigated.

Methods: iPS-CM were differentiated and purified from murine iPS cells expressing GFP and α-myosin-induced puromycin resistance, while naïve cardiomyocytes (NMC) were obtained from neonatal mouse hearts. The simulated in vitro ischemia model consisted of 3 h hypoxia (1%O2) and glucose/serum deprivation. Cell damage was quantified by caspase 3/7, 8 and 9 activation, TUNEL and 7-Aminoactinomycin D presentation (7-AAD), visualization of the mitochondrial potential (JC-1), metabolic activity (MTS test) and ATP measurement. Activation of intracellular signaling cascades was evaluated by qRT-PCR and Western blotting. Finally, the protective effect of multipotent stromal cell-conditioned medium on iPS-CM and NMC in simulated ischemia was assessed.

Results: In response to simulated ischemia, 48 ± 5% iPS-CM and 23 ± 3% NMC displayed poly-caspase activation (p < 0.01), with a similar pattern for individual activities of caspase 3/7, 8 and 9. Ten ± 3% iPS-CM and 2.7 ± 0.1% NMC were 7-AAD positive (p = 0.02), while the proportion of TUNEL-positive cells was similar. The average mitochondrial membrane potential was reduced in iPS-CM as compared with normoxic cells, but remained unchanged in NMC. The MTS conversion rate was significantly more reduced in “ischemic” iPS-CM than in NMC (p = 0.001), as was the average cellular ATP content (p = 0.01). Transcriptional upregulation of heat shock protein 70 (Hsp70) was blunted in iPS-CM compared to NMC, as was the phosphorylation of STAT3 and PKCε. MSC-conditioned medium restored metabolic activity in iPS-CM and NMC to similar extent (p < 0.05 vs. normoxia, intergroup p = 0.6), but only iPS-CM reacted also with a significant increase in ATP synthesis (p < 0.05)

Conclusions: The response of iPS-CM to simulated ischemia is not identical to that of naïve cardiomyocytes. It remains to be determined whether this is a reprogramming-induced phenomenon or a reflection of cellular maturity. Concomitant treatment with MSC conditioned medium may help improve the iPS-CM resistance to ischemia.