Key physiological phenomena governing transgene expression based on tissue pressure-mediated transfection in mice

It is generally recognized that in vivo gene transfection is one of the most important techniques used in the post-genome era. Above all, naked plasmid DNA transfection has attracted much attention because of its advantages including convenience of preparation and handling and lack of toxicity associated with the transfection agents. We have investigated tissue pressure-mediated transfection performed by light and controlled pressure of the target tissue after normal intravenous injection of plasmid DNA. So far, we have demonstrated that plasmid DNA and small-interfering RNA (siRNA) are very efficiently transfected into murine kidney, liver and spleen without causing marked tissue damage. In this study, in order to understand the key physiological phenomena affecting transgene expression, we performed a set of experiments involving tissue pressure-mediated transfection, including the biodistribution and cellular transport of plasmid DNA and activation of transcriptional factors and obtained the following results: i) plasmid DNA transfer to the target tissue and its cells increased although the transferred fraction was small compared to the total administered plasmid DNA, ii) a transient increase in cellular translocation of plasmid DNA was induced, and iii) transcriptional factors were activated. Taking all these results into consideration, it would appear that tissue pressure-mediated transfection enhances plasmid DNA transfer to the target tissue and its cells and also activation of the transcriptional process. This information will allow a better understanding of in vivo transgene expression based on naked plasmid DNA transfection involving tissue pressure-mediated transfection.