Physiological and histological changes in skeletal muscle following in vivo gene transfer by electroporation

Abstract

Electroporation (EP) is used to transfect skeletal muscle fibers in vivo, but its effects on the structure and function of skeletal muscle tissue have not yet been documented in detail. Methods We studied the changes in contractile function and histology after EP to determine the mechanism of recovery, the extent of myofiber damage, and the efficiency of expression of a green fluorescent protein (GFP) transgene in the tibialis anterior (TA) muscle of adult male C57Bl/6J mice. Results Immediately after EP, contractile torque decreased by ~ 80% from pre-EP levels. Within 3 hr, torque recovered to ~ 50% but stayed low until day 3. Functional recovery progressed slowly and was complete at day 28. In muscles depleted of satellite cells by X-irradiation, torque remained low after day 3, suggesting that myogenesis is necessary for complete recovery. In unirradiated muscle, myogenic activity after EP was confirmed by an increase in fibers with central nuclei or developmental myosin. Damage after EP was confirmed by the presence of necrotic myofibers infiltrated by CD68+ macrophages, which persisted in electroporated muscle for 42 days. Expression of GFP was detected at day 3 after EP and peaked on day 7, with ~ 25% of fibers transfected. The number of fibers expressing GFP, the distribution of GFP+ fibers, and the intensity of fluorescence in GFP+ fibers were highly variable. We conclude that EP of murine TA muscles produces highly variable and low levels of transgene expression, and causes extensive damage that requires myogenesis for recovery.