Effects of Different Terahertz Frequencies on Gene Expression in Human Keratinocytes

In recent years, a surge in the development of many terahertz (THz) sensing and imaging technologies occurred leading to increased use in military and civil operations. Therefore, understanding the biological effects associated with exposures to this radiation is becoming increasingly important. Previous studies have speculated that cells exposed to different frequencies of THz radiation may exhibit differential responses. However, empirical studies to confirm such differences have not been performed. The question of whether cells exposed to different THz frequencies exhibited specific biological responses remains unclear. In this study, we exposed human keratinocytes to a THz laser tuned to several different THz frequencies using our recently developed THz exposure system. This system consists of an optically pumped molecular gas THz laser source coupled to a modified cell culture incubator permitting THz radiation exposures under controlled standard tissue culture conditions. For all frequencies, we matched the THz exposure duration and irradiance. During THz exposure, we monitored the power as DC voltage-logged values (LabVIEW (TM) IV log). To determine the temperature changes by THz exposure, we collected temperature readings from the unexposed and THz-exposed cells using thermocouples. We assessed cellular viability after exposure using MTT colorimetric assays. We compared the changes in gene expression profiles using messenger RNA (mRNA) microarrays, and we identified the THz-induced signaling pathways for each frequency using bioinformatics. Our data provide valuable new insights that give a comparative picture of the genes and intracellular signaling pathways triggered in cells exposed to THz radiation at different frequencies.