Red Light Modulates Ultraviolet-Induced Gene Expression in the Epidermis of Hairless Mice

Objective: The purpose of this study was to investigate whether low-level light therapy (LLLT) was capable of modulating expression of ultraviolet (UV) light-responsive genes in vivo. Materials and methods: The effects of 670nm light-emitting diode (LED) array irradiation were investigated in a hairless SHK-1 mouse epidermis model. Mice were given a single dose of UVA/UVB light, or three doses of red light (670nm @ 8mW/cm(2) x 312sec, 2.5J/cm(2) per session) spread over 24h along with combinations of pre- and post-UV treatment with red light. Levels of 14UV-responsive mRNAs were quantified 24h after UV irradiation by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Results: The transcription of mRNAs encoding for cluster of differentiation molecule 11b (CD11b) (p<0.05) and interferon (IFN)- (p<0.012) increased after irradiation with red light alone, whereas expression level of cyclooxygenase (COX)-2 (p<0.02) was downregulated. Genes unresponsive to UV did not change their expression levels after exposure to red light either. Pretreatment with red light significantly modified response of Fos to UV exposure (p<0.01). A synergy of UV and post-treatment with red light in reducing the transcription levels of CD11b (p<0.05) and inducible nitric oxide synthase (iNOS) (p<0.05) was observed. Conclusions: This is an initial observation that in mouse red light LLLT more often than not causes opposite gene expression changes or reduces those caused by moderate UVA-UVB irradiation.