A human skin explant model to study molecular changes in response to fractional photothermolysis: Spatio-temporal expression of HSP70

Abstract

Background and objectives

Ablative fractional photothermolysis (AFP) is a new concept to treat aged skin. Despite growing clinical experience, little is known about the molecular changes induced over time by AFP in the targeted skin compartments. This is due, in part, to difficulties in obtaining multiple skin biopsies from AFP-treated individuals. In an attempt to circumvent these limitations, a human skin explant model was designed. In order to test its suitability as a model to study molecular changes induced by AFP, the spatio-temporal expression of heat shock protein 70 (HSP70) has been investigated in response to AFP at different pulse energies.

Materials and methods

AFP was performed using a scanned 250 μm CO₂-laser beam. The ablative single pulse energies were set to 50, 64 and 300 mJ at 150 ablation zones per cm². The immediate response to AFP, as well as a response 1, 3 or 7 days after AFP, was studied; untreated skin explants served as a control. Additionally, intradermal injections of transforming growth factor β (TGF-β) on day 0 served as a positive control for HSP70 induction in non-laser-treated samples, cultivated over 7 days. A routine pathology workup and immunohistochemistry (HSP70) was performed in all untreated (control group and positive control samples) and AFP-treated samples. In summary, a total of 245 samples were investigated.

Results

In this explant model, HSP70 showed a clear time-dependent induction by AFP with expression profile being most prominent in the epidermis, a marked up-regulation at 1 h following AFP, peaking between 1 and 24 h post-treatment, only then to decline significantly within the following 7 days.

Conclusion

The human skin explant model can be used to bridge the gap between in vitro cell culture experiments and in vivo investigations to study the spatio-temporal effects of AFP on human skin. Specifically, CO₂-laser AFP of skin explants resulted in an energy-dependent, short-lived up-regulation of HSP70 expression predominantly in the epidermal compartment.