Mechanistic Approaches to the Light-Induced Neural Cell Differentiation: Photobiomodulation vs Low-Dose Photodynamic Therapy

Physical Stimulation Methods Developed for In Vitro Neuronal Differentiation Studies of PC12 Cells: A Comprehensive Review

PC12 cells, which are derived from rat adrenal pheochromocytoma cells, are widely used for the study of neuronal differentiation. NGF induces neuronal differentiation in PC12 cells by activating intracellular pathways via the TrkA receptor, which results in elongated neurites and neuron-like characteristics. Moreover, the differentiation requires both the ERK1/2 and p38 MAPK pathways. In addition to NGF, BMPs can also induce neuronal differentiation in PC12 cells. BMPs are part of the TGF-β cytokine superfamily and activate signaling pathways such as p38 MAPK and Smad. However, the brief lifespan of NGF and BMPs may limit their effectiveness in living organisms. Although PC12 cells are used to study the effects of various physical stimuli on neuronal differentiation, the development of new methods and an understanding of the molecular mechanisms are ongoing. In this comprehensive review, we discuss the induction of neuronal differentiation in PC12 cells without relying on NGF, which is already established for electrical, electromagnetic, and thermal stimulation but poses a challenge for mechanical, ultrasound, and light stimulation. Furthermore, the mechanisms underlying neuronal differentiation induced by physical stimuli remain largely unknown. Elucidating these mechanisms holds promise for developing new methods for neural regeneration and advancing neuroregenerative medical technologies using neural stem cells.

Investigation of the optimal light parameters for photobiomodulation to induce osteogenic differentiation of the human bone marrow stem cell and human umbilical vein endothelial cell co-culture

Bones have an important role in the human body with their complex nature. Mesenchymal stem cells and endothelial cells together support their unique and complex nature. Photobiomodulation (PBM) is a promising method that provides cell proliferation, osteogenic differentiation, and bone regeneration. However, there are still unknowns in the mechanism of osteogenic differentiation induced by PBM. The main aim of the study is to understand the molecular mechanism of PBM at 655 and 808 nm of wavelengths and identify the most effective energy densities of both wavelengths for osteogenic differentiation. The effect of PBM on osteogenic differentiation of Human Bone Marrow Stem Cell (hBMSC) and Human Umbilical Vein Endothelial Cell (HUVEC) co-culture was examined at 1, 3, and 5 J/cm2 energy densities of red and near-infrared light through different analysis such as cell viability, scratch assay, intracellular reactive oxygen species production, and ATP synthesis, nitric oxide release, temperature monitoring, and osteogenic differentiation analyses. Even though all PBM-treated groups exhibited better results compared to the control group, 5 J/cm2 energy density induced faster cell proliferation and migration at both wavelengths. The increases in ATP and NO levels as signaling molecules, and the increases in DNA, ALPase, and calcium contents as osteogenic markers were higher in the groups treated with 5 J/cm2 energy density at both wavelengths. Only a slight change was obtained in the level of intracellular ROS after any light applications. It can be concluded that NO release has a very important role together with ATP production in PBM therapy to trigger DNA synthesis, ALPase activity, and mineralization for osteogenic differentiation of the hBMSC and HUVEC co-culture at 655 and 808 nm of wavelengths.

Synergistic effects of integrin binding peptide (RGD) and photobiomodulation therapies on bone-like microtissues to enhance osteogenic differentiation

Bone tissue engineering aims to diversify and enhance the strategies for bone regeneration to overcome bone-related health problems. Bone mimetic peptides such as Gly-Arg-Gly-Asp-Ser (RGD) are useful tools for osteogenic differentiation. Similarly, photobiomodulation (PBM) at 600-800 nm of wavelength range improves bone tissue healing via the production of intracellular reactive oxygen species (ROS), ATP synthesis, and nitric oxide (NO) release. Besides, traditional monolayer cell culture models have limited conditions to exhibit the details of a mechanism such as a peptide or PBM therapy. However, scaffold-free microtissues (SFMs) can mimic a tissue more properly and be an efficient way to understand the mechanism of therapy via cell-cell interaction. Thus, the synergistic effects of RGD peptide (1 mM) and PBM applications (1 J/cm² energy density at 655 nm of wavelength and 5 J/cm² energy density at 808 nm of wavelength) were evaluated on SFMs formed with the co-culture of Human Bone Marrow Stem Cells (hBMSC) and Human Umbilical Vein Endothelial Cells (HUVEC) for osteogenic differentiation. Cell viability assays, mechanistic analysis, and the evaluation of osteogenic differentiation markers were performed. Combined therapies of RGD and PBM were more successful to induce osteogenic differentiation than single therapies. Especially, RGD + PBM at 655 nm group exhibited a higher capability of osteogenic differentiation via ROS production, ATP synthesis, and NO release. It can be concluded that the concomitant use of RGD and PBM may enhance bone regeneration and become a promising therapeutic tool to heal bone-related problems in clinics.

Photobiomodulation therapy at red and near-infrared wavelengths for osteogenic differentiation in the scaffold-free microtissues

One of the novel strategies for bone tissue regeneration is photobiomodulation (PBM) which depends on the red and near-infrared light absorption by mitochondria and may trigger bone tissue regeneration via the production of intracellular ROS and ATP, NO release, etc. It is also important to identify the changes in those signal molecule levels in an in vivo mimicking platform such as 3-Dimensional (3D) Scaffold Free Microtissues (SFMs) that may serve more natural osteogenic differentiation responses to PBM. Herein, we aimed to increase the osteogenic differentiation capability of the co-culture of Human Bone Marrow Stem Cells (hBMSC) and Human Umbilical Vein Endothelial Cells (HUVECs) on 3D SFMs by triple light treatment at 655 and 808-nm of wavelengths with the energy densities of 1, 3, and 5 J/cm². We performed the analysis of cell viability, diameter measurements of SFMs, intracellular ROS production, NO release, ATP activity, temperature measurements, DNA content, ALPase activity, calcium content, and relative gene expressions of ALP, Collagen, and Osteopontin by qRT-PCR. It was found that both wavelengths were effective in terms of the viability of SFMs. 1 and 5 J/cm² energy densities of both wavelengths increased the SFM diameter with significant changes in intracellular ROS, ATP, and NO levels compared to the control group. We concluded that PBM therapy was successful to induce osteogenesis. 1 J/cm² at 655 nm of wavelength and 5 J/cm² at 808 nm of wavelength were the most effective energy densities for osteogenic differentiation on SFMs with triple light treatment.