NF-kB related transgene expression in mouse tibial cranial muscle after pDNA injection followed or not by electrotransfer

BACKGROUND

When activated, NF-κB can promote the nuclear import and transcription of DNA possessing NF-κB consensus sequences. Here, we investigated whether NF-κB is involved in the plasmid electrotransfer process.

METHODS

Mouse tibial cranial muscles were transfected with plasmids encoding luciferase bearing or not NF-κB consensus sequences. Luciferase transgene expression was evaluated noninvasively by luminescence imaging and the number of pDNA copies in the same muscles by qPCR. RT-PCR of heat shock protein HsP70 mRNA evidenced cell stress. Western blots of phosphorylated IkBα were studied as a marker of NF-κB activation.

RESULTS

Intra-muscular injection of a plasmid bearing a weak TATA-like promoter results in a very low muscle transfection level. Electrotransfer significantly increased both the number of pDNA copy and the transgene expression of this plasmid per DNA copy. Insertion of NF-κB consensus sequences into pDNA significantly increased the level of gene expression both with and without electrotransfer. Electrotransfer-induced cellular stress was evidenced by increased HsP70 mRNA. Phosphorylated IκBα was slightly increased by simple pDNA injection and a little more by electrotransfer. We also observed a basal level of phosphorylated IκBα and thus of free NF-κB in the absence of any stimulation.

GENERAL SIGNIFICANCE

pDNA electrotransfer can increase transgene expression independently of NF-κB. The insertion of NF-κB consensus sequences into pDNA bearing a weak TATA-like promoter leads to enhanced transgene expression in muscle with or without gene electrotransfer. Finally, our results suggest that the basal amount of free NF-κB in muscle might be sufficient to enhance the activity of pDNA bearing NF-κB consensus sequences.

Safe and efficient local gene delivery into skeletal muscle via a combination of Pluronic L64 and modified electrotransfer

Efficient DNA electrotransfer into muscles can be achieved by combining two types of electronic pulses sequentially: short high-voltage (HV) pulse for the cell electropermeabilization and long low-voltage (LV) pulse for the DNA electrophoresis into cells. However, the voltages currently applied can still induce histological and functional damages to tissues. Pluronic L64 has been considered as a molecule possessing cell membrane-disturbing ability. For these reasons, we hope that L64 can be used as a substitute for the HV pulse in cell membrane permeabilization, and a safe LV pulse may still keep the ability to drive plasmid DNA across the permeabilized membrane. In this work, we optimized the electrotransfer parameters to establish a safe and efficient procedure using a clinically applied instrument, and found out that the critical condition for a successful combination of electrotransfer with L64 was that the injection of plasmid/L64 mixture should be applied 1 h before the electrotransfer. In addition, we revealed that the combined procedure could not efficiently transfer plasmid into solid tumor because the uncompressed plasmid may rapidly permeate the leaky tumor vessels and flow away. Altogether, the results demonstrate that the combined procedure has the potential for plasmid-based gene therapy through safe and efficient local gene delivery into skeletal muscles.