Heat shock-induced three-dimensional-like proliferation of mouse fibroblasts mediated by hydroxyapatite

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The aim of this study was to determine the minimal conditions in which heat treatment is effective for and the optimal heat conditions for enhancing three-dimensional (3D)-like cell proliferation. C3H10T1/2 mouse fibroblasts were cultured with hydroxyapatite granules for 10 weeks after heat treatment at 40, 41.5, 43, 44 or 45℃ for 2, 10, 15, 20, 30, 45, 60, 90, 180 and 360 min. Then minimal and optimal conditions of temperature and duration of heat treatment for induction of 3D-like proliferation of cells were determined. The minimal conditions of heat treatment to induce 3D-like proliferation were 43℃ for 2 min and the optimal conditions were 43℃ for 10 min. The mean rates of formation of 3D-like proliferation patterns by cells heat-treated at 43℃ for 2 and 10 min were significantly higher (1.7-and 3.7-fold higher, respectively) than that by untreated cells (p < 0.05). We also observed significantly greater effects of heat treatment on 3D-like proliferation at 40℃ for 90 or 180 min and at 41.5℃for 15 min and 44℃ for 10 min. We found that apoptosis had occurred in 7.5% and 87.0% of the cells at one week after heat treatment at 43℃ for 10 min and 30 min, respectively. Western blot analysis demonstrated that phosphorylation of p38 mitogen-activated protein kinase (MAPK) was markedly increased by heat treatment at 43℃ for 10 min. These findings suggest that activation of p38 MAPK by heat shock is associated with 3D-like cell proliferation. The results of this study should be useful for further studies aimed at elucidation of the physiologic mechanisms underlying thermotherapy and hyperthermia.