Comparison of Repeated Doses of C-kit-Positive Cardiac Cells versus a Single Equivalent Combined Dose in a Murine Model of Chronic Ischemic Cardiomyopathy

PU.1 inhibition does not attenuate cardiac function deterioration or fibrosis in a murine model of myocardial infarction

Activated cardiac fibroblasts are involved in both reparative wound healing and maladaptive cardiac fibrosis after myocardial infarction (MI). Recent evidence suggests that PU.1 inhibition can enable reprogramming of profibrotic fibroblasts to quiescent fibroblasts, leading to attenuation of pathologic fibrosis in several fibrosis models. The role of PU.1 in acute MI has not been tested. We designed a randomized, blinded study to evaluate whether DB1976, a PU.1 inhibitor, attenuates cardiac function deterioration and fibrosis in a murine model of MI. A total of 44 Ai9 periostin-Cre transgenic mice were subjected to 60 min of coronary occlusion followed by reperfusion. At 7 days after MI, 37 mice were randomly assigned to control (vehicle) or DB1976 treatment and followed for 2 weeks. Left ventricular ejection fraction (EF), assessed by echocardiography, did not differ between the two groups before or after treatment (final EF, 33.3 ± 1.0% in control group and 31.2 ± 1.3% in DB1976 group). Subgroup analysis of female and male mice showed the same results. There were no differences in cardiac scar (trichrome stain) and fibrosis (interstitial/perivascular collagen; picrosirius stain) between groups. Results from the per-protocol dataset (including mice with pre-treatment EF < 35% only) were consistent with the full dataset. In conclusion, this randomized, blinded study demonstrates that DB1976, a PU.1 inhibitor, does not attenuate cardiac functional deterioration or cardiac fibrosis in a mouse model of MI caused by coronary occlusion/reperfusion.

Effects of Heme Oxygenase-1 on c-Kit-Positive Cardiac Cells

Heme oxygenase-1 (HO-1) is one of the most powerful cytoprotective proteins known. The goal of this study was to explore the effects of HO-1 in c-kit-positive cardiac cells (CPCs). Lin^NEG/c-kit^POS CPCs were isolated and expanded from wild-type (WT), HO-1 transgenic (TG), or HO-1 knockout (KO) mouse hearts. Compared with WT CPCs, cell proliferation was significantly increased in HO-1^TG CPCs and decreased in HO-1^KO CPCs. HO-1^TG CPCs also exhibited a marked increase in new DNA synthesis during the S-phase of cell division, not only under normoxia (21% O₂) but after severe hypoxia (1% O₂ for 16 h). These properties of HO-1^TG CPCs were associated with nuclear translocation (and thus activation) of Nrf2, a key transcription factor that regulates antioxidant genes, and increased protein expression of Ec-SOD, the only extracellular antioxidant enzyme. These data demonstrate that HO-1 upregulates Ec-SOD in CPCs and suggest that this occurs via activation of Nrf2, which thus is potentially involved in the crosstalk between two antioxidants, HO-1 in cytoplasm and Ec-SOD in extracellular matrix. Overexpression of HO-1 in CPCs may improve the survival and reparative ability of CPCs after transplantation and thus may have potential clinical application to increase efficacy of cell therapy.