Strength and muscle specificity of a compact promoter derived from the slow troponin I gene in the context of episomal (gutless adenovirus) and integrating (lentiviral) vectors

Background Gutless adenovirus (helper-dependent adenoviral vector; HDAd) and lentiviral vectors (LV) are attractive vectors for the gene therapy of muscle diseases. Because the organization of their DNA (episomal versus integrated) differs, we investigated whether the strength and specificity of Delta USEx3, a novel muscle-specific promoter previously tested with plasmid, were maintained in the context of these vectors. Methods Two HDAds expressing beta-galactosidase regulated by Delta USEx3 or CAG [cytomegalovirus (CMV) enhancer/beta-actin promoter], and three LV expressing green fluorescent protein regulated by Delta USEx3, CMV or a modified skeletal alpha-actin promoter (SPc Delta 5-12), were constructed. Gene expression was compared in cell culture and after intravenous (HDAd only) and intramuscular injection of mice. Results Irrespective of the vector used,Delta USEx3 remained poorly active in nonmuscle cells and tissues. In myotubes, Delta USEx3 was as strong as CMV and SPc Delta 5-12, although it was ten-fold weaker than CAG, a proven powerful promoter in muscle. In cell culture, Delta USEx3 activity in the context of LV was more stable than CMV, indicating it is less prone to silencing. In the context of HDAd, the behavior of Delta USEx3 in skeletal muscle mirrored that of cell culture (10% of the CAG activity and half the number of transduced fibers). Surprisingly, in muscles treated with LV, Delta USEx3 activity was five-fold lower than SPc Delta 5-12. Conclusions The data obtained in the present study confirm that Delta USEx3 is a strong and robust muscle-specific promoter in the context of HDAd (cell culture and in vivo) and LV (cell culture). However, it was less efficient in vivo in the context of LV. Copyright (C) 2012 National Research Council Canada & John Wiley & Sons, Ltd.