A histochemical and radiobiological study of in vitro and in vivo human epithelial cell rest proliferation

Epithelial cell rests from periodontal ligament in vitro and epithelial trabeculae in apical granulomata were studied. The epithelial lining of dental cysts was also examined because of its probable origin from proliferated cell rest epithelium. Proliferated cell rests were obtained by culturing periodontal ligament explants in a closed culture system with McCoy's medium. DNA synthesis in this epithelium was confirmed by labelling explants with tritiated thymidine. A characteristic feature of the proliferated cells was their greatly increased amount of cytoplasm. Proliferated cell rest epithelium in vitro and in vivo exhibited little succinic dehydrogenase activity and contained no glycogen. However, lactic dehydrogenase and glucose-6-phosphate dehydrogenase activity was readily demonstrable. Lipid accumulation was a characteristic feature of proliferated epithelium. These findings are interpreted to formulate the thesis that in response to local environmental change, probably to change in oxygen/carbon dioxide tension, epithelial cells proliferate and are able to do so by virtue of their ability to undertake anaerobic glycolysis. It is suggested that endogenous protein synthesis required for cell multiplication is brought about partly by pentose shunt activity which is, in turn, linked with lipid synthesis.