Engineered cardiac tissue might enable novel therapeutic strategies for the human heart in a number of acquired and congenital diseases. With recent advances in stem cell technologies, namely the availability of pluripotent stem cells, the generation of potentially autologous tissue grafts has become a realistic option. Nevertheless, a number of limitations still have to be addressed before clinical application of engineered cardiac tissue based on human stem cells can be realized. We summarize current progress and pending challenges regarding the optimal cell source, cardiomyogenic lineage specification, purification, safety of genetic cell engineering, and genomic stability. Cardiac cells should be combined with clinical grade scaffold materials for generation of functional myocardial tissue in vitro. Scale-up to clinically relevant dimensions is mandatory, and tissue vascularization is most probably required both for preclinical in vivo testing in suitable large animal models and for clinical application. Graphical Abstract.
Objectives: CD133pos cells are currently evaluated for use in cardiac cell therapy. We hypothesized that they exert their beneficial effects in a paracrine manner and investigated this in a cell culture ischaemia model. Furthermore, we checked whether purified CD133pos cells perform better than non-fractionated mononuclear cells (MNC). Methods: CD133pos cells were isolated from bone marrow MNC and conditioned medium was prepared from CD133pos and non-fractionated MNC. HL-1 cardiomyocytes were subjected to simulated ischaemia in the respective conditioned media or in control medium. After treatment, total remaining cells, apoptotic cells and nuclear shrinking were quantified using an automated imaging system. Furthermore, metabolic activity and phosphorylation of kinases Akt, Erk1/2, GSK3b and transcription factor Stat3 were investigated. Results: After simulated ischaemia, the rate of detached dead cells was lowest in CD133pos conditioned medium (26 ± 6%) and highest in control medium (36 ± 6%). In CD133pos conditioned medium, the fraction of nonapoptotic cells was most enhanced and nuclear shrinking as a consequence of apoptosis was reduced. Cell viability was also highest in CD133pos conditioned medium (109.4 ± 8.8% in relation to control). In both conditioned media, phosphorylation of Akt, Erk1/2, and GSK3b was lower than in control medium. Stat3 phosphorylation was sustained on the level of control. Conclusions: Factors released from purified CD133pos bone marrow cells exhibit more pronounced protective effects on HL-1 cardiomyocytes under simulated ischaemia than from non-fractionated MNC. These effects are not associated with the phosphorylation of cell survival promoting kinases Akt, Erk1/2, GSK3b and transcription factor Stat3. Although the molecular mechanism of cardioprotection by CD133pos cells requires further investigation, our results reinforce the advantage of enriching CD133pos cells for cardiac cell therapy.
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