In vivo and in vitro rapid cold-hardening protects cells from cold-shock injury in the flesh fly

The capacity to undergo rapid the cold-hardening response (RCH) has been documented in diverse groups of insects and functions to protect against non-freezing cold injury and to preserve physiological performance in response to environmental cooling. The RCH response is remarkable for the rapidity of its induction; however the mechanism by which insects perceive cold and transduce this input at the cellular level has received little attention. To test the hypothesis that cells from isolated tissues can undergo RCH in response to cold, we assessed cell viability in four tissues that had undergone either RCH (0degreesC, 2 h followed by -8degreesC, 2 h) or cold-shock (-8degreesC, 2 h) both in vivo and in vitro from the adult flesh fly Sarcophaga crassipalpis (Diptera: Sarcophagidae) using fluorescent probes. Adult flies showed a significantly higher survival rate in the RCH group than in the cold-shocked group. Similarly, in all tissues tested, both in vivo and in vitro, RCH significantly improved cell survival compared with the respective cold-shocked groups. To our knowledge this is the first report to demonstrate that isolated cells and tissues from insects can undergo RCH. These results indicate that insect cells are capable of cold-sensing without neuroendocrine mediation; direct induction at the cellular level also helps to explain the swiftness of the RCH response.