Abstract
MAPCs are pluripotent cells derived from mesenchymal stromal cells (MSCs) in adult bone marrow. In contrast to MSCs, MAPCs differentiate into various lineages of mesodermal, ectodermal and endodermal origin, and contribute to numerous terminally differentiated tissues in the recipients. This capacity is enhanced in the setting of injury, suggesting a possible role of MAPCs in repair and regeneration in disease states. We aimed to investigate the capacity of MAPCs to aid in myocardial repair in hearts with postinfarction remodeling. We reasoned that as MAPCs differentiate to both endothelium and cardiomyocytes in vitro and as engraftment of delivered cells depends on establishing adequate blood flow in the ischemic region, MAPCs may represent the optimal cell type to contribute to both angiogenesis and the parenchymal tissue to regenerate function of injured myocardium. To study engraftment and survival of MAPCs, we labeled adult murine C57BL/6 MAPCs with firefly luciferase and DsRed2 fluorescent protein using non-viral Sleeping Beauty transposons, and injected them into myocardium of C57BL/6 adult mice with acute myocardial infarction (AMI). Mice were anesthetized, intubated and mechanically ventilated using a small-animal respirator. Under a stereomicroscope the heart was accessed via left thoracotomy. The left anterior descending coronary artery was ligated at mid-level between apex and base with a 9-0 surgical suture to produce AMI. Twenty minutes later, intramyocardial injections of labeled MAPCs in saline, or saline alone were administered at five distinct injection sites at boarder zone of AMI (total MAPC dose = 106/mouse). Chest was closed in layers and animals were allowed to recover. Mice were followed with echocardiography and in vivo whole body bioluminescent imaging. Seventy days after AMI, MAPCs recipients (N=6) had significantly less severe left ventricular (LV) dilatation evidenced by a smaller LV end-diastolic and LV end-systolic dimensions when compared to control mice infused with saline (N=4) (average±standard deviation, 4.7±0.2 mm versus 5.3±0.5 mm, p=0.05; and 3.7±0.2 mm versus 4.4±0.6 mm, p=0.03, respectively). In addition, ejection and shortening fractions were significantly higher in MAPC recipients (36±2% versus 30±3%, p=0.004; and 20±1% versus 16±2%, p=0.004, respectively). Luciferase signals emitted from donor MAPCs were easily detectable in MAPC recipients 100 days after MAPC infusion, at which point the animals were harvested. Analyses are ongoing to determine whether MAPCs and their progeny contributed to expansion of coronary vasculature (capillary density), or formed or modified injured myocardial tissue. Alternatively, both populations of repair cells could have been derived from donor (DsRed2+) MAPCs, or donor MAPCs could have provided permissive local environment to recruit recipient cells and enhance endogeneous regeneration. In summary, these findings provide evidence that MAPCs persist long term in injured myocardium and document the potential of MAPCs for improvement of cardiac function after ischemic myocardial injury. Jakub Tolar and Xiaohong Wang contributed equally to this study.
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