Abstract
Mesenchymal stromal cells (MSCs) are multipotent cells present in adult bone marrow that replicate as undifferentiated cells and can differentiate to lineages of mesenchymal tissues. Here, I show that laser irradiation can direct the osteogenesis of MSCs by altering the intracellular localization of the circadian rhythm protein Cryptochrome (CRY). After laser irradiation (wavelength: 405 nm) to MSCs, circadian rhythm proteins CRY1 and PER2 were immunostained and histochemical stainings for osteogenic differentiation were observed. Laser irradiation promoted osteogenesis of MSCs, induced the translocation of CRY1 and PER2 proteins from the cytoplasm to the nucleus, and decreased mCRY1 mRNA levels quantified by real-time PCR. Since the timing of nuclear accumulation of clock proteins constitutes an important step in the transcription-translation feedback loop driving the circadian core oscillator, laser irradiation could provide a simple and effective technology for clock protein localization and turnover. However, I believe that the mechanism of cell differentiation by laser irradiation is not so simple. In this article, I propose that cell differentiation is regulated by intracellular photoreceptors, such as CRY, cytochrome c oxidase, and porphyrin, and reactive oxygen species (ROS), etc. after laser irradiation. The detailed mechanism should be clarified by using molecular biology based techniques.
