Heat shock protein 70 expression induced by diode laser irradiation on choroid-retinal endothelial cells in vitro

PURPOSE To investigate the biologic effect of an 810 nm diode laser on the induction of heat shock protein 70 (Hsp70) in choroid-retinal endothelial cells in vitro. METHODS Cultured rhesus macaque choroid-retinal endothelial cells (RF/6A) were irradiated using an 810 nm diode laser (spot size, 10 mm; duration, 60 s; power, 400-1,500 mW). Cell viability was assessed by annexin V- fluorescein isothiocyanate (FITC) and propidium iodide flow cytometric assay. Hsp70 expression was determined by western blot at 6, 12, 18, 24, and 48 h following laser exposure. Intracellular distribution of Hsp70 was examined by immunofluorescence staining. RESULTS The laser-induced cell injury threshold was found to be at a power of 1,100 mW power (fluence, 84.08 J/cm(2)), above which there was significant cell death. Under this power, Hsp70 expression elevated obviously and was stronger at 600-1,000 mW power settings (fluences, 45.86-76.43 J/cm(2)). The expression of Hsp70 peaked at 12-18 h postirradiation, and returned to baseline by 48 h. Immunofluorescence staining indicated the induced Hsp70 expression in both the cytoplasm and the nucleus. CONCLUSIONS Subthreshold 810 nm diode laser exposure can induce Hsp70 hyperexpression from 12 to 18 h postirradiation in cultured choroid-retinal endothelial cells without obvious cell death. The results could be useful for investigating and designing more effective laser therapies.