Figure 6

Schematic for arrest and utilization of autophagy in normal mesenchymal stem cell (MSC) function. As evidenced by transmission electron microscopy images and green fluorescent protein-red fluorescent protein tracking of light chain 3 in this study, undifferentiated MSCs appear to exist at a state of high basal autophagy, with many autophagosomes in a state of arrest in the cytosol (left). Artificial activation of autophagosome degradation with rapamycin (right) leads to a rapid clearance of existing autophagosomes in the cell, with subsequent rough endoplasmic reticulum (RER) enlargement, suggesting a potential advantage for MSCs to mobilize autophagy during times of high energy demand. Thus, during a time such as differentiation or nutrient starvation (bottom), a similar phenotype is observed in the cells whereby arrested autophagosomes in the cell are mobilized and degraded, allowing the MSCs to proceed in the differentiation process or potentially resist negative effects of stressors. mTOR, mammalian target of rapamycin.