Cardiac Mesenchymal Cells Cultured at Physiologic Oxygen Tension Have Superior Therapeutic Efficacy in Heart Failure Caused by Myocardial Infarction.

Stem/progenitor cells are usually cultured at atmospheric O2 tension (21%); however, since physiologic O2 tension in the heart is ∼5%, using 21% O2 may cause oxidative stress and toxicity. Cardiac mesenchymal cells (CMCs), a newly discovered and promising type of progenitor cells, are effective in improving left ventricle (LV) function after myocardial infarction (MI). We have previously shown that, compared with 21% O2, culture at 5% O2 increases CMC proliferation, telomerase activity, telomere length, and resistance to severe hypoxia in vitro. However, it is unknown whether these beneficial effects of 5% O2 in vitro translate into greater therapeutic efficacy in vivo in the treatment of heart failure. Thus, murine CMCs were cultured at 21% or 5% O2. Mice with heart failure caused by a 60-min coronary occlusion followed by 30 days of reperfusion received vehicle, 21% or 5% O2 CMCs via echocardiography-guided intraventricular injection. After 35 days, the improvement in LV ejection fraction effected by 5% O2 CMCs was > 3 times greater than that afforded by 21% O2 CMCs (5.2 vs. 1.5 units, P < 0.01). Hemodynamic studies (Millar catheter) yielded similar results both for load-dependent (LV dP/dt) and load-independent (end-systolic elastance) indices. Thus, two independent approaches (echo and hemodynamics) demonstrated the therapeutic superiority of 5% O2 CMCs. Further, 5% O2 CMCs, but not 21% O2 CMCs, significantly decreased scar size, increased viable myocardium, reduced LV hypertrophy and dilatation, and limited myocardial fibrosis both in the risk and non-infarcted regions. Taken together, these results show, for the first time, that culturing CMCs at physiologic (5%) O2 tension provides superior therapeutic efficacy in promoting cardiac repair in vivo. This concept may enhance the therapeutic potential of CMCs. Further, culture at 5% O2 enables greater numbers of cells to be produced in a shorter time, thereby reducing costs and effort and limiting cell senescence. Thus, the present study has potentially vast implications for the field of cell therapy.

Myocardial Reparative Properties of Cardiac Mesenchymal Cells Isolated on the Basis of Adherence.

BACKGROUND: The authors previously reported that the c-kit-positive (c-kitPOS) cells isolated from slowly adhering (SA) but not from rapidly adhering (RA) fractions of cardiac mesenchymal cells (CMCs) are effective in preserving left ventricular (LV) function after myocardial infarction (MI). OBJECTIVES: This study evaluated whether adherence to plastic alone, without c-kit sorting, was sufficient to isolate reparative CMCs. METHODS: RA and SA CMCs were isolated from mouse hearts, expanded in vitro, characterized, and evaluated for therapeutic efficacy in mice subjected to MI. RESULTS: Morphological and phenotypic analysis revealed that murine RA and SA CMCs are indistinguishable; nevertheless, transcriptome analysis showed that they possess fundamentally different gene expression profiles related to factors that regulate post-MI LV remodeling and repair. A similar population of SA CMCs was isolated from porcine endomyocardial biopsy samples. In mice given CMCs 2 days after MI, LV ejection fraction 28 days later was significantly increased in the SA CMC group (31.2 ± 1.0% vs. 24.7 ± 2.2% in vehicle-treated mice; p < 0.05) but not in the RA CMC group (24.1 ± 1.2%). Histological analysis showed reduced collagen deposition in the noninfarcted region in mice given SA CMCs (7.6 ± 1.5% vs. 14.5 ± 2.8% in vehicle-treated mice; p < 0.05) but not RA CMCs (11.7 ± 1.7%), which was associated with reduced infiltration of inflammatory cells (14.1 ± 1.6% vs. 21.3 ± 1.5% of total cells in vehicle and 19.3 ± 1.8% in RA CMCs; p < 0.05). Engraftment of SA CMCs was negligible, which implies a paracrine mechanism of action. CONCLUSIONS: We identified a novel population of c-kit-negative reparative cardiac cells (SA CMCs) that can be isolated with a simple method based on adherence to plastic. SA CMCs exhibited robust reparative properties and offered numerous advantages, appearing to be more suitable than c-kitPOS cardiac progenitor cells for widespread clinical therapeutic application.