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.