Thermotolerance and Profile of Protein Synthesis in Murine Bone Marrow Cells after Heat Shock

In this study, we first investigated the survival of colony-forming units, granulocyte and macrophage (CFU-GM), after a single heat treatment. We then examined the induction, development, and decay of thermotolerance in CFU-GM. Finally, we analyzed the profiles of protein synthesis in the total murine bone marrow population during the development of thermotolerance. Several salient features emerged from our study: (a) granulocyte-macrophage progenitors were very sensitive to heat as compared to other mammalian cell lines; (b) CFU-GM can develop thermotolerance after both prolonged heating at 41-42°C or an acute heat treatment at 43°C in vitro; (c) thermotolerance in CFU-GM can be induced in vivo; the kinetics of development of thermotolerance in vivo is similar to that in vitro\ (d) in contrast to other cell lines where thermotolerance lasts for several days, tolerance acquired by CFU-GM disappeared within 24 h, regardless of the temperature or duration of the initial heat treatment. The difference between the kinetics of systemic thermotolerance and thermotolerance in CFU-GM in the same animal model shows that bone marrow stem cells, or at least CFU-GM, are not the critical targets for systemic thermal death. When protein synthesis profiles of the heat-shocked bone marrow cells were compared to those from nonheated controls by one- and two-dimensional gel electrophoresis, the rates of synthesis of the Mr 70,000 and 87,000 proteins were shown to be enhanced during the development of thermotolerance. The enhanced rate of synthesis of these polypeptides lasted only 2-4 h and then returned to the control value.