Efficient, glucose responsive, and cell-specific transgene expression in pancreatic islets.
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Diabetes mellitus is increasing in prevalence, affecting more than 5% of the population throughout the world. Novel therapeutic strategies, including new medications, islet transplantation, and gene therapy, are vigorously being sought to treat diabetes. Direct in vivo pancreatic gene delivery targeting the islets is a key approach for diabetic gene therapy. So far studies have shown that the adenovirus, adeno-associated virus, lentivirus, and herpes simplex virus-1 vectors can be used for efficient gene transfer to the islets in vivo, but suffered from host immune responses and vector cytotoxicity. Non-viral gene delivery systems, including naked DNA and DNA complexes, have also demonstrated islet cell transfection at much lower levels and with transient transgene expression over time. However, it seems likely that non-viral vector systems will more easily satisfy bio-safety concerns in clinical trials. Our new gene therapy approach, ultrasound-targeted micro-bubble destruction (UTMD), has shown that it is able to deliver genes to the pancreas in vivo. Briefly, genes are incorporated into cationic liposome and then attached to the phospholipids shell of gas-filled micro-bubble, which are then injected intravenously and destroyed within the microcirculation of intact islets by ultrasound. This approach enables transfection of the entire islet core, wherein most beta cells reside. Our current study focuses on how to construct gene therapy vectors that can drive functional gene expression in beta cells efficiently. We now demonstrate differential efficiency of gene expression by varying the length of the RIP segments. We attempted to expand the insulin gene promoter from the traditional area to the non-coding region in exon1, intron1 and part of exon2 of the rat insulin gene 1 with a downstream reporter gene in the plasmid construction. We report that UTMD delivers this rat insulin promoter driving the reporter vectors to intact islets of adult, living animals, providing a relative safety, tissue-specific, high efficient and regulated gene expression for diabetic gene therapy.