Enhanced gene transfer into skeletal muscle by electroporation in neonatal mice

Abstract

Local delivery of electric pulses is an efficient technology for muscle transfection with foreign gene in vivo. We examined the efficiency of naked DNA transfer into skeletal muscle by in vivo electroporation in neonates. We used pCMV-EGFP as the expression vector. Ten μg of plasmid DNA were injected into the biceps of neonatal 7-day-old C57BL/6 mice. Immediately after the injection, electric pulses were delivered with a square wave electroporator transcutaneously. Ten pulses were delivered and the duration of the each pulse was 500 ms, with 500 ms interpulse delay. Various values of voltage were tested. One day after the operation, the muscle fibers did not express EGFP neither in the electroporated nor nonelectroporated groups. Application of electric pulses with 50V increased the number of EGFP expressing muscle fibers by 68 folds 3 days after the operation, in comparison with non-electroporated muscle. The enhancement of EGFP expression declined to 49 and 42 folds 7 and 14 days, respectively, following the operation. Twenty-eight days after operation, there were only few EGFP expressing muscle fibers in the electroporated group, whereas no EGFP positive fibers were observed in the nonelectroporated group. Delivery of electric pulses at either 10V or 900V was significantly less efficient in enhancing the expression of EGFP in neonatal muscle fibers. Our results indicate that significant enhancement of foreign gene expression in vivo can be achieved in neonatal muscles. This is crucial for the development of gene therapy and the developmental studies of spinomuscular neurodegenerative diseases. Supported by a grant from Hong Kong Research Grants Council HKU7254/98M & HKU7024/99M