Direct Reprogramming of Fibroblasts in a Failing Heart Improves Cardiac Function

Introduction and aims: Adult mammalian myocardium holds little to no regenerative potential following injury. Cardiac fibroblasts account for a majority of the cells in the heart, poses an inert ability to proliferate thus representing an attractive target for cardiac regeneration. Recent studies, done immediately after coronary artery occlusion in mice, have shown that viral delivery of 3 developmental cardiac transcription factors, Gata4, Mef2c and Tbx5 (GMT) prevents cardiac deterioration, by direct reprograming of cardiac fibroblasts into cardiomyocyte-like cells. However, it remains unknown whether this strategy reverses cardiac fibrosis and remodeling in an already infarcted heart.

Methods and results: As a first step toward a clinical application of direct reprogramming approach, we delivered the GMT vector directly into the heart using a cationic polymer, in vivo jetPEI transfection reagent, rather than a common viral delivery. As confirmed by RT-PCR and Western blot, all three transcription factors exhibited higher expression level as compared to control. Next, we aimed to explore whether direct reprogramming of the GMT using jetPEI may reverse fibrosis and improve cardiac function in failing hearts. Toward this end we performed a permanent occlusion of the LAD in female rats. Seven days after the occlusion, a few animals were euthanized for histological analysis confirming the persistence of a fibroblast-induced scar in the ischemic territory. The rest were treated with GMT vector or jetPEI only as a control and subjected to further analysis. Three weeks later, echocardiography analysis revealed a significant improvement in cardiac systolic function and decreased LV hypertrophy, in GMT-treated animals compared with controls.

Conclusions: We have shown that GMT delivery to the infracted tissue improves cardiac function and attenuates the post-infarction compensatory hypertrophy which is a common outcome of a heart failure, suggesting a new therapeutic strategy to reverse cardiac fibrosis and improve outcome in heart failure patients.