The application of NIR to optogenetic systems is in great demand due to its superior properties enabling in vivo deep tissue penetration. Irradiation of NIR to tissue samples or cells rapidly generates heat locally. The resultant elevation in temperature affects cells at the molecular level because of the activation of the heat shock pathway and ROS generation. Nevertheless, few reports have presented detailed comparisons of the effects of the temperature change rate on signaling pathway biomolecules, especially those of rapid heat changes. Aiming at broadening the understanding of temperature sensitivity, we investigated seven insulin signaling pathway biomolecules (INSR, IRS1, Akt, GSK3β, p70S6K, FoxO1, and ERK1/2) in three cell lines (C2C12, HepG2, and Fao) at temperatures between 25 and 45 °C. The results show that, except for INSR, pAkt(T308), and FoxO1, biomolecules are sensitive to rapid temperature changes at temperatures higher than 42 °C, at which they are significantly phosphorylated. At 25 °C, around a 50% reduction in phosphorylation occurred. Moreover, p70S6K is sensitive over time. It dephosphorylates quickly (5 min) and then phosphorylates over time. Our findings extend the temperature range to 45 °C, while providing additional time course information about the signaling pathway biomolecule response necessary to advance NIR optogenetic research.
Keywords: NIR; insulin signaling; optogenetics; temperature.