Far infrared ray irradiation attenuates apoptosis and cell death of cultured keratinocytes stressed by dehydration

Far infrared (FIR) irradiation has been widely applied in health promotion. The aims of this study were to investigate the protective effect of FIR irradiation on stressed keratinocytes and the signaling pathways involved. HaCaT was subjected to sorbitol dehydration with or without 40 min pretreatment with FIR radiation 4 h earlier. Western blots of cell lysates were analyzed for caspase-3, HO-1, BCL2, Bax, ERK, and Akt. The incidence of apoptosis was also assessed by TUNEL staining. Evaluation of cell viability was determined using MTT. mRNAs were extracted and compared using Illumina Human Ref-8 v2 BeadChips. Hyperosomotic injury of HaCaT cells caused by sorbitol resulted in increased cleaved caspase-3 expression and this effect was decreased by FIR pretreatment; these findings were confirmed by TUNEL staining and MTT tests. Pre-treatment with FIR irradiation before sorbitol-induced dehydration significantly upregulated phosphorylated Akt (p-Akt) levels and A6730, an Akt kinase inhibitor (5 μM), attenuated the protective effect of FIR irradiation. A microarray study showed FIR irradiation had far less effect at the transcriptional level. FIR pretreatment attenuates apoptosis and cell death in dehydration-stressed cultured keratinocytes through the PI-3K/Akt pathway, this protective effect of FIR irradiation is not at the transcriptional level.