Model systems to investigate the effect of cholesterol on the transfection efficiency of lipoplexes

Motivated by its important role in lipid-mediated gene delivery, we have studied the effect of cholesterol on membrane fusion. While recent work in our group has identified the membrane charge density as a critical parameter for transfection efficiency (TE) of lamellar, DOPC containing cationic lipid-DNA (CL-DNA) complexes [1-3], this model cannot fully explain the effect of cholesterol, suggesting that a different mechanism is responsible for the observed enhancement of TE. A model system using negatively charged giant vesicles has been developed to mimic the interaction of the cell membrane with CL-DNA complexes containing cholesterol. Differences in fusogenic properties have been observed as a function of the amount of cholesterol present in the CL-DNA complexes, and a fluorescence resonance energy transfer based assay was employed to quantify this effect. X-ray diffraction confirms that the lamellar structure seen with CL- DNA complexes is retained with the addition of cholesterol. Funding provided by NIH GM-59288 and NSF DMR-0503347. [1] A.J. Lin et al, \textit{Biophys. J.}, 2003, V84:3307-3316. [2] K. Ewert et al, \textit{J. Med. Chem.}, 2002, V45:5023-5029. [3] A. Ahmad et al., \textit{J. Gene Med., }2005, V7:739-748.