细胞生物学

This protocol aims to study intercellular transport of mitochondria, dynamic cellular organelles via tunnelling nanotubes (TNT), a cell membrane extension of cytoskeletal elements. The nanotubular bridges or the tunnelling nanotube highways are one of the emerging new cell-to-cell communication systems which mediates exchange of cellular materials, most importantly as in our observation, mitochondria. Mesenchymal stem cells (MSC) have been well studied to be endowed with a highly efficient intercellular mitochondrial donation ability and this property is now proven crucial to its functional role of rescue in cellular therapy.

This assay makes use of the dye Acridine Orange (AO) to determine the stability of lysosomes in living cells upon exposure to a confocal microscope laser.

AO is a lipophilic amine that readily diffuses into cells (Figure 1). Inside the cell it enters the acidic lysosomal compartment where it is protonated and sequestered, shifting its emission spectrum towards a longer wavelength (i.e. red). Once inside the lysosomes, the metachromatic AO sensitizes the lysosomal membrane to photo-oxidation by blue light (Brunk et al., 1997). Upon light-induced loss of the lysosomal pH gradient and subsequent leakage of AO into the cytosol, the emission spectrum of AO shifts from red to green (Figure 2). Hence, loss of lysosomal integrity can be measured as a ‘loss of red dots’ or as a quantitative rise in green fluorescence (Petersen et al., 2010; Kirkegaard et al., 2010; Petersen et al., 2013).


Figure 1. Acridine Orange


Figure 2. Snapshots visualizing the U2OS cells at various steps of the recording procedure (Petersen et al., 2010)