Green light photobiomodulation modulates the temporal expression of neural and glial markers in mesenchymal stem...

Photobiomodulation (PBM) using light-emitting diodes (LEDs) has emerged as a promising approach to enhance differentiation potential of mesenchymal stem cells (MSCs). However, the temporal dynamics of neural-lineage marker expression following LED irradiation remain poorly understood. This study investigated the time-dependent effects of green LED irradiation on neural differentiation of human umbilical cord matrix-derived mesenchymal cells (hUCMs). Cells were exposed to green LED irradiation (530 nm, 1.59 J/cm²), retinoic acid (RA), and their combination (RA + LED). The expression of neural-lineage markers was evaluated by qRT-PCR and immunocytochemistry at days 7, 14, and 21 following neural induction of hUCMs. Green LED irradiation induced an early progenitor response, with nestin expression increasing on days 7 and 14 before declining by day 21. β-tubulin III and MAP2 showed transient increases, with the highest expression of β-tubulin III observed on day 14, particularly in the RA + LED group, whereas MAP2 expression increased primarily at days 7 and 14. Among the glial markers examined, Olig2 exhibited a delayed rise (days 14 and 21) in the LED and RA + LED groups, while GFAP increased in the RA and RA + LED groups at several time points. Overall, RA + LED treatment enhanced both the magnitude and timing of marker expression, making MAP2 and β-tubulin III responses earlier and more potent, but delaying the increase in glial-associated markers. These findings demonstrate that green LED-mediated PBM regulates neural-lineage commitment in a time-dependent manner, suggesting that day 14 may represent a favorable time point for harvesting preconditioned MSCs.