Enhanced real-time monitoring of adeno-associated virus trafficking by virus-quantum dot conjugates

The unique spectral properties of semiconductor quantum dots (QDs) enable long-term live-cell imaging and ultrasensitive detection of viral particles, which in turn can potentially provide a practical means for detailed analysis of the underlying molecular mechanisms of virus entry. In this study, we report a general method of labeling adeno-associated virus serotype 2 (AAV2) with QDs for enhanced visualization of the intracellular behavior of viruses in living target cells. It was found that the mild conditions required for this QD conjugation reaction allowed for the retention of viral infectivity of AAV2. Furthermore, quantitative analysis of viral motility in living cells suggested that QD-labeling had no significant effect on the intracellular transport properties of AAV2 particles compared to those of conventional organic dye-labeled AAV2. Our imaging study demonstrated that QD-AAV2 was internalized mainly through a clathrin-dependent pathway and then trafficked through various endosomes. It was also observed that QD-AAV2 particles exploit the cytoskeleton network to facilitate their transport within cells, and the labeling study provided evidence that the ubiquitin-proteasome system was likely involved in the intracellular trafficking of AAV2, at least at the level of nuclear transport. Taken together, our findings reveal the potential of this QD-labeling method for monitoring the intracellular dynamics of virus-host cell interactions and interrogating the molecular mechanisms of viral infection in greater detail.