Heat stress induces alkaline phosphatase activity and heat shock protein 25 expression in cultured pulp cells

To investigate the responses of cultured rat pulp cells to heat stress.

Pulp cells were obtained from rat incisors and cultured at 37 degrees C. The cells were cultured at 42 degrees C for 30 min and then cultured at 37 degrees C again. Morphology, alkaline phosphatase (ALP) activity and expression of heat shock protein 25 (HSP25) were investigated at 0, 1, 3, 5, 7, 10 and 14 days following stimulation. As a control, the cells were maintained at 37 degrees C.

Although there were few cells of apoptosis immediately after heat stress, there were mitotic cells from day 1 after heat stress. ALP activity in the heat stress group significantly increased at days 7 and 14 compared with the control group (about 1.7-fold, P < 0.01, Friedman test). HSP25 expression increased in both groups, with HSP25 in the heat stress group being expressed earlier than in the control group, and nuclear localization of HSP25 was observed at days 0 and 1 in heat-stressed cells.

These results suggest that heat stress not only induces HSP25 but also enhances ALP activity in pulp cells.