Application of microscopical techniques in the study of autolysosome dynamics in PC12 neurites

Autophagy is a principal degradation pathway for the turnover of intracellular proteins or cytoplasmic organelles in response to starvation. During autophagic activation, autophagosomes fuse with lysosomes to form autolysosomes where incorporated materials are degraded. However, the dynamics of autolysosomes in neurites of live cells was still poorly known. In this study, various subsets of microscope were applied to analyse the autophagy induction and highly dynamic transport of autolysosomes in rat PC12 neurites. Beading formation was found in degenerating PC12 neurites under phase contrast light microscope after serum deprivation. The monomeric red fluorescence protein-green fluorescence protein-light chain 3-labelled autolysosomes accumulated throughout PC12 neurites after 18 h of serum deprivation as revealed by fluorescence microscope analysis. The single-membrane autolysosomes were also visualized in PC12 cells under transmission electron microscope. Moreover, fluorescence recovery after photobleaching experiment, which was conducted by confocal laser scanning microscope, demonstrated that autolysosomes were motile vesicles and moved along PC12 neurites during starvation. The directional transport of monomeric red fluorescence protein -labelled autolysosomes in neurites was further monitored by a motorized video microscope. Both anterograde and retrograde transport of autolysosomes were observed. In addition, the autolysosomes were precisely mapped by using 2D Gaussian fitting and then their highly dynamic movement was robustly tracked by using multidimensional assignment. Collectively, by using different microscopical techniques, our results confirmed the dynamic transport of autolysosomes in starved PC12 neurites and may provide valuable insight into understanding the biophysical characteristics of autolysosomes in neurites under physiological and pathological conditions.