Gene electrotransfer into murine skeletal muscle: a systematic analysis of parameters for long-term gene expression.

Skeletal muscle is an attractive target tissue for delivery of therapeutic genes, since it is well vascularized, easily accessible, and has a high capacity for protein synthesis. For efficient transfection in skeletal muscle, several protocols have been described, including delivery of low voltage electric pulses and a combination of high and low voltage electric pulses. The aim of this study was to determine the influence of different parameters of electrotransfection on short-term and long-term transfection efficiency in murine skeletal muscle, and to evaluate histological changes in the treated tissue. Different parameters of electric pulses, different time lags between plasmid DNA injection and application of electric pulses, and different doses of plasmid DNA were tested for electrotransfection of tibialis cranialis muscle of C57Bl/6 mice using DNA plasmid encoding green fluorescent protein (GFP). Transfection efficiency was assessed on frozen tissue sections one week after electrotransfection using a fluorescence microscope and also noninvasively, followed by an in vivo imaging system using a fluorescence stereo microscope over a period of several months. Histological changes in muscle were evaluated immediately or several months after electrotransfection by determining infiltration of inflammatory mononuclear cells and presence of necrotic muscle fibers. The most efficient electrotransfection into skeletal muscle of C57Bl/6 mice in our experiments was achieved when one high voltage (HV) and four low voltage (LV) electric pulses were applied 5 seconds after the injection of 30 microg of plasmid DNA. This protocol resulted in the highest short-term as well as long-term transfection. The fluorescence intensity of the transfected area declined after 2-3 weeks, but GFP fluorescence was still detectable 18 months after electrotransfection. Extensive inflammatory mononuclear cell infiltration was observed immediately after the electrotransfection procedure using the described parameters, but no necrosis or late tissue damage was observed. This study showed that electric pulse parameters, time lag between the injection of DNA and application of electric pulses, and dose of plasmid DNA affected the duration of transgene expression in murine skeletal muscle. Therefore, transgene expression in muscle can be controlled by appropriate selection of electrotransfection protocol.

Sequence and time dependence of transfection efficiency of electrically-assisted gene delivery to tumors in mice.

Electrically-assisted gene delivery is a non-viral gene delivery technique, using application of square wave electric pulses to facilitate uptake of plasmid DNA into the cells. Feasibility and effectiveness of this method in vivo was already demonstrated, elaborating on pulse parameters and plasmid construction. However, there were no studies performed on sequencing and timing of plasmid DNA injection into the tumors and application of electric pulses. For this purpose we measured luciferase expression in two tumor models (LPB fibrosarcoma, B16F1 melanoma) after electrically-assisted gene delivery at varying time intervals between the pCMV-Luc plasmid injection and electroporation. Expression of luciferase was determined by measurement of its activity using luminometer. The results demonstrated that pCMV-Luc plasmid has to be injected before the application of electric pulses, since no measurable expression was detected in the tumors when pCMV-Luc plasmid was injected after electroporation of tumors. In both tumor models the highest transfection efficiency was obtained when pCMV-Luc plasmid was injected not less than 5 minutes but also not more than 30 minutes before the application of electric pulses. The results also demonstrated variability in the transfection efficiency depending on the tumor model. High expression was obtained in B16F1 tumor model (approximately 5500 pg luc/mg tumor) and lower in LPB fibrosarcoma (approximately 200 pg luc/mg tumor). In conclusion, our results demonstrate that regardless of the susceptibility of the tumors to electrically-assisted gene delivery, the best timing for pCMV-Luc plasmid is between 30 to 5 minutes prior to the application of electric pulses to the tumors.

Posttranslational modification of 6-phosphofructo-1-kinase in Aspergillus niger.

Two different enzymes exhibiting 6-phosphofructo-1-kinase (PFK1) activity were isolated from the mycelium of Aspergillus niger: the native enzyme with a molecular mass of 85 kDa, which corresponded to the calculated molecular mass of the deduced amino acid sequence of the A. niger pfkA gene, and a shorter protein of approximately 49 kDa. A fragment of identical size also was obtained in vitro by the proteolytic digestion of the partially purified native PFK1 with proteinase K. When PFK1 activity was measured during the proteolytic degradation of the native protein, it was found to be lost after 1 h of incubation, but it was reestablished after induction of phosphorylation by adding the catalytic subunit of cyclic AMP-dependent protein kinase to the system. By determining kinetic parameters, different ratios of activities measured at ATP concentrations of 0.1 and 1 mM were detected with fragmented PFK1, as with the native enzyme. Fructose-2,6-biphosphate significantly increased the Vmax of the fragmented protein, while it had virtually no effect on the native protein. The native enzyme could be purified only from the early stages of growth on a minimal medium, while the 49-kDa fragment appeared later and was activated at the time of a sudden change in the growth rate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of sequential purifications of PFK1 enzymes by affinity chromatography during the early stages of the fungal development suggested spontaneous posttranslational modification of the native PFK1 in A. niger cells, while from the kinetic parameters determined for both isolated forms it could be concluded that the fragmented enzyme might be more efficient under physiological conditions.