Wavelength-dependent dynamics of heat shock protein 70 expression in free electron laser wounds

摘要

Many medical laser procedures require selecting laser operating parameters that minimize undesirable tissue damage. In this study, heat shock protein 70(hsp70) gene expression was used as a sensitive marker for laser-induced thermal damage. Wound repair and hsp70 expression were compared after surgery with the free electron laser(FEL) as a function of wavelength(λ) and radiant exposure(H). Damage was assessed at λ = 6.45, 6.10, and 2.94 μm using 8-20 J/cm~2. The FEL beam (ω_r=200 μm,30Hz, τ_p =5μs) was delivered to produce a 6.5 mm square wound. hsp70 expression was assessed using a transgenic mouse strain with the hsp70 promoter driving luciferase and eGFP expression. Bioluminescent imaging (BLI) was monitored non-invasively and in real time. Hsp70 protein was visualized with laser confocal imaging, blood velocity was measured with 2D-laser doppler, and depth of tissue damage was measured using histological methods. BLI verified the model's sensitivity and peak hsp70 expression was bi-phasic, with maxima occurring 12 and 24 hours after FEL irradiation. hsp70 expression exhibited wavelength-dependence, and it increased with radiant exposure. Histology indicated that tissue damage at 6.45 μm was ～2x deeper than 6.10 μm. Quantitative BLI with the Hsp70-luc transgene can be used to non-invasively measure gene expression in laser-tissue interaction studies.