Myocardial injury-induced fibroblast proliferation facilitates retroviral-mediated gene transfer to the rat heart in vivo.

Abstract

Efficient and stable transfer of therapeutic DNA into injured myocardium would be an initial step towards a genetic treatment aimed at myocardial repair after myocardial infarction. Proliferating cardiac fibroblasts in the healing myocardium could be a compelling target for retroviral infection. We evaluated the feasibility of direct in vivo gene transfer into injured myocardium using a high-titer, stable retroviral vector. Using the TE-FLY-A-based MFG retroviral vector harboring nlsLacZ reporter, the gene transfer efficiency was assessed first in vitro in rat cardiac fibroblasts, followed by in vivo evaluation in healing rat myocardium after local freeze-thaw injury. A total of 2.5 x 10(7) infectious units of retrovirus were injected into the injured region of a beating rat heart. The transduced cells were identified by X-gal staining and immunohistochemistry. Highly efficient transduction of cardiac fibroblasts was observed in vitro with 98% of the cells transduced with single infection. The cell proliferation index in the cardiac granulation tissue appeared maximal 3 days after cryoinjury. Retroviral injection into the injured beating heart induced gene expression localized to the wound repair region. One week after retrovirus injection, 14% of the cells in the reparative tissue were beta-gal-positive, while 4% were beta-gal-positive after 4 weeks. The transduced cells were mostly myofibroblasts. Local gene transfer to the healing rat heart is feasible by retrovirus in vivo. This observation may serve as a useful guide for the development of gene therapy aimed at myocardial repair after myocardial infarction.