Adeno-associated virus (AAV)-7 and-8 poorly transduce vascular endothelial cells and are sensitive to proteasomal degradation

Transduction of the vascular endothelium by adeno-associated virus (AAV) vectors would have broad appeal for gene therapy. However, levels of transduction by AAV serotype-2 are low, an observation linked to deficiencies in endothelial cell binding, sequestration of virions in the extracellular matrix and/or virion degradation by the proteasome. Strategies to improve transduction of endothelial cells include AAV-2 capsid targeting using small peptides isolated by phage display or the use of alternate serotypes. Previously, we have shown that AAV serotypes-3 through-6 transduce endothelial cells with poor efficiency. Recently, AAV serotypes-7 and -8 have been shown to mediate efficient transduction of the skeletal muscle and liver, respectively, although their infectivity profile for vascular cells has not been addressed. Here, we show that AAV-7 and -8 also transduce endothelial cells with poor efficiency and the levels of transgene expression are markedly enhanced by inhibition of the proteasome. In both cases proteasome blockade enhances the nuclear translocation of virions. We further show that this is vascular cell-type selective since transduction of smooth muscle cells is not sensitive to proteasome inhibition. Analysis in intact blood vessels corroborated these findings and suggests that proteasome degradation is a common limiting factor for endothelial cell transduction by AAV vectors.