Ectopic Cardiogenic Transcription Factor Expression Augments the Anti‐fibrogenic Activity of Administered Cardiac Mesenchymal Stromal Cells in a Model of Chronic Ischemic Cardiomyopathy

Preclinical studies suggest that donor cell cardiomyogenic lineage commitment may be an important determinant of the efficacy of cardiac mesenchymal stromal cell (CMC) therapy; however, to what extent myogenic commitment influences CMC cardiac reparative capacity, as well as the underlying mechanisms by which they promote cardiac functional recovery remains poorly defined. In the current study we examine the consequences of enhanced cardiomyogenic lineage commitment on CMC cardiac reparative capacity in vivo and paracrine signaling potency in vitro, via ectopic expression of core cardiogenic transcription factors GMT (GMT: GATA4, MEF2C, and TBX5). Rat CMCs transduced with a tricistronic lentiviral construct harboring GMT coding sequences, or green fluorescent protein (GFP) control, were intramyocardially delivered in a rat model of chronic ischemic cardiomyopathy 30 days after a reperfused myocardial infarction. Indices of cardiac function were assessed by echocardiography and left ventricular (LV) Millar conductance catheterization 35 days after treatment. Infarct size and myocardial collagen deposition were enumerated in coronal‐dissected, cardiac tissue sections by Masson's trichrome or picrosirius red staining, respectively. Cytokine array analyses and in vitro cardiac fibroblast activation assays were performed using conditioned medium (CoMed) derived from either GMT or GFP CMCs, to respectively assess cardiotrophic factor secretion and anti‐fibrogenic paracrine signaling potential. Compared to GFP controls, GMT CMCs exhibited superior ability to attenuate LV systolic dysfunction and myocardial fibrosis in vivo. Proteome cytokine array analyses of CoMed revealed enhanced expression of cytokines with GMT CMCs that function in pathways that regulate matrix remodeling and collagen catabolism. Further, CoMed harvested from GMT CMCs more robustly inhibited Col1A1 synthesis in TGFβ1 activated cardiac fibroblast assays in vitro, compared to that of GFP CMCs. These results provide direct evidence that CMC myogenic lineage commitment biases cardiac repair and, further, that enhanced anti‐fibrogenic paracrine signaling potency may underlie, in part, their improved therapeutic utility.