Survival of Exfoliated Epithelial Cells: A Delicate Balance between Anoikis and Apoptosis

Figure 1

The concept of epithelial functional unit. The flow chart summarizes the cellular status of epithelial cells recovered by dietary palmitate on intestinal renewal (left panel) or by cycles of fasting/refeeding on gastric exfoliation (right panel). As shown in central panel, epithelial cell functional units are organized in four compartments (stem cells, proliferative, terminally differentiated, senescent). The isolation of exfoliated cells is dependent on the techniques (manual or induced by some stress), the epithelium itself, the health status and the species. A major difference in the autophagy/phagocytosis process of senescent cells has been found between rat or mouse-exfoliated colonocytes which are lost in the lumen and human colonocytes which are rarely lost in the lumen but actively recycled by neighboring cells [15]. Quiescent epithelial cells can be isolated from different body fluids (breast milk, urines, and digestives fluids). They are believed to enter rapidly in anoikis after exfoliation. Anoikis is considered as an autophagic state promoting epithelial cell survival after a timely loss of contact with extracellular matrix and cell neighbors [16]. Primary cultures can be derived from breast milk indicating that some phenotypes retain clonogenic potentials. Molecular components of circadian clocks are detected in these cells like in any other somatic cells and could provide molecular data on the expression ratios between these proteins provided sampling procedures are standardized. Further work is needed to check for any different rates of exfoliation according to the time of day, seasons, and to differences in phenotypes.