The role of heat shock protein 70 in laser irradiation and thermal preconditioning

Abstract

Lasers have taken on an ever-expanding role in the medical field for diagnostic and therapeutic applications. Commonly, damage from laser procedures has been quantified on the tissue level. As a result, relatively little knowledge has been gathered about the cellular level of sub-lethal damage. In reality, damaged cells undergo a complex reformation of their underlying biochemistry when pathways are activated and suppressed in response to heat damage. We used a cell culture system and a molecular biology approach to study laser induced sub-lethal cellular damage. Our approach incorporated three key components to interrogate the character and function of HSP70, which is one of the most well know mediators of thermal stress in cells. First a bioluminescent transgene system was used wherein the luciferase reporter gene is expressed upon activation of the Hsp70 promoter and light is emitted. The changes in bioluminescence correlated to the level of thermal stress within the cells. We showed that exposing cells to a mild thermal insult prior to more severe heat shock significantly increased cell survival. Using a 'knockout' cell line that has the Hsp70 gene deleted, we showed that the efficacy of this preconditioning treatment was greatly reduced in the absence of HSP70 protein. However, some thermotolerance was still present. Consequently, a gene expression analysis was carried out to determine the other genes that are involved in the cellular response to thermal stress. The methods used in this research allowed us a unique window into the molecular workings of the cell on a fundamental level that may eventually translate to clinical applications involving thermal responses.