Thermotolerance of pulp cells and phagocytosis of apoptotic pulp cells by surviving pulp cells following heat stress.

Apoptosis is known to be associated with wound healing and regeneration of dental pulp. We examined the effects of heat stress on clonal dental pulp cell line (RPC-C2A cells) to clarify the pulp wound healing process. RPC-C2A cells were exposed to heat stress at 43 degrees C for 45 min. After several time intervals, the inhibition of cell proliferation and apoptosis induction were analyzed by cell viability assay, DNA gel electrophoresis, nuclear staining, and terminal deoxynucleotidyl transferase mediated labeling assay. RPC-C2A cells showed the thermotolerance following heat stress. We found that apoptosis was induced in some RPC-C2A cells, whereas others remained alive, and observed the engulfment of apoptotic cells by scavenger-like RPC-C2A cells following heat stress. We also analyzed the phagocytotic activity of RPC-C2A cells and found that they had an ability to engulf apoptotic RPC-C2A cells, which was stimulated by heat stress. These results suggest that heat stress induces apoptosis of RPC-C2A cells, which are phagocytosed by the surviving RPC-C2A cells.