Introduction: Ventricular remodelling following myocardial infarction is strongly associated with inflammation, mainly mediated by macrophages. In contrast to the M1 polarized type of macrophages, the M2 type macrophage has been described to exhibit potent regenerative and anti-inflammatory characeristics. Since mesenchymal stem cells (MSC) can influence the M1/M2 polarization of macrophages, we tested MSC mediated M2 macrophage specific effects in a small animal model of myocardial infarction.

Objectives: The effects of co-transplanting mesenchymal stem cells (MSC) with cardiomyocytes derived from induced pluripotent stem cells (iPS-CM) were examined in a murine model of myocardial infarction. Methods: Immediately after myocardial cryo-infarction, mice were subjected to intramyocardial injections into the peri-infarction area of either: a) enhanced green fluorescent protein (EGFP) and luciferase-expressing iPS CM, b) para-magnetically-labelled MSC, c) a combination of both or d) saline. Bioluminescent imaging (iPS CM) or magnetic resonance imaging (MSC) was used to track transplanted cells. Left ventricular ejection fraction (LVEF) was assessed by magnetic resonance imaging. Size of infarction scar and structural integration of transplanted cells were analysed histologically. Results: Relative bioluminescence intensity of transplanted iPS CM was decreased to 43 ± 7% on day 1 and further to 18 ± 2% on day 28 for iPS-CM and to 49 ± 11% on day 1 and 19 ± 2% on day 28 for iPS CM + MSC. Transplanted MSC were detectable in the peri-infarct region of the left ventricular wall up to four weeks. LVEF increased significantly in a) iPS-CM, 51.8 ± 3.3% and c) iPS CM/MSC, 55.7 ± 2.3%, compared to b) MSC, 47.6 ± 1.9%, both P < 0.001, and d) saline, 44.2 ± 2.6%, both P < 0.001 after four weeks. Infarct scar size was significantly decreased in a) iPS-CM, 2.77 ± 1.35 mm2 and c) iPS-CM/MSC, 2.73 ± 1.18 mm2 compared to b) MSC, 4.9 ± 1.79 mm2, both P < 0.05, and d) saline, 5.73 ± 2.68 mm2, both P < 0.05. Structurally organized expression of cardiac α-actinin-2 and connexin-43 was detected in transplanted iPS CM indicating cardiogenic maturation. Conclusions: Intramyocardial co-transplantation of iPS CM and MSC improved recovery of heart function and reduced infarct scar size, confirming the significant potential of this approach for regenerative therapies.

Introduction: The combined transplantation of mesenchymal stem cells (MSC), mediating paracrine effects, together with cardiomyocytes generated from induced pluripotent cells (iPS-CM), mediating functional effects, holds great promise in cardiac cell therapy. The goal of this study was to analyze how functional improvement of infarcted hearts is mediated on a histological level in a small animal model.

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.