Conditions affecting direct gene transfer into rodent muscle in vivo

This report extends our previous findings that mouse muscle cells in situ can take up naked DNA injected intramuscularly in vivo. Various conditions such as needle type, speed of injection, volume of injection fluid, tonicity of injection fluid, type of solute, type of muscle, physiologic condition of the muscle and age of the animals were appraised for their effect on the levels of luciferase activity expressed from the pRSVL plasmid. Specific conditions such as the use of normal saline as an injection fluid increased the efficiency of expression. The implantation of DNA pellets was an effective way to deliver DNA to muscle, especially for smaller muscle groups. Also, newborn and adult rat muscles expressed plasmid DNA delivered intramuscularly.

Direct gene transfer and expression into rat heart in vivo

We found previously that genes injected into skeletal muscle can be taken up by myofibers and expressed. In the present study we found that myocardial cells can also express a variety of reporter genes injected into myocardium as efficiently as skeletal myofibers, while the cells of several other tissues cannot. The inability of tissues other than striated muscle to express injected DNA is not due to technical difficulties of injection because injected DNA was detected in these other tissues by PCR analysis. These results suggest that skeletal and cardiac muscle cells have unique features such as T tubules that may play a critical role in DNA uptake. Expression in cardiac muscle was stable for only two weeks, possibly because of an immune response against the transfected cells. The ability to directly transfer genes into myocardial cells raises the possibility of gene therapy for both acquired and genetic heart diseases.

Direct gene transfer into mouse muscle in vivo

RNA and DNA expression vectors containing genes for chloramphenicol acetyltransferase, luciferase, and beta-galactosidase were separately injected into mouse skeletal muscle in vivo. Protein expression was readily detected in all cases, and no special delivery system was required for these effects. The extent of expression from both the RNA and DNA constructs was comparable to that obtained from fibroblasts transfected in vitro under optimal conditions. In situ cytochemical staining for beta-galactosidase activity was localized to muscle cells following injection of the beta-galactosidase DNA vector. After injection of the DNA luciferase expression vector, luciferase activity was present in the muscle for at least 2 months.