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. Homeostatic control of bone remodelling maintains bone mass by insuring that bone resorption and bone formation occur sequentially and in a balanced manner. As most homeostatic functions occur in a circadian manner, a circadian clock could control bone mass. Here, we show that laser irradiation can direct the osteogenesis and adipogenesis of mouse MSCs by altering the intracellular localization of the circadian rhythm protein Cryptochrome 1 (mCRY1). After laser irradiation (wavelength: 405 nm) to MSCs, circadian rhythm protein, mCRY1 and mPER2, were immunostained and histochemical stainings for osteogenic or adipogenic differentiation were observed. Laser irradiation promoted osteogenesis and reduced adipogenesis of MSCs, induced the translocation of mCRY1 and mPER2 protein 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. Our results also indicate that mCRY1 is a master regulator of circadian rhythm that regulates the differentiation of MSCs. Laser irradiation could provide a simple and effective means of controlling the fate of MSCs as a therapeutic strategy and act 'molecular switch' of regulatory proteins by suppressing CRY transcription. Furthermore, this model system may be useful for exploring the crosstalk between circadian rhythm and cell differentiation.