Low-Level Laser Irradiation Stimulates RANKL-Induced Osteoclastogenesis via the MAPK Pathway in RAW 264.7 Cells

Jae-Min Song,Bong-Soo Park,In-Ryoung Kim,Sang-Hun Shin

doi:10.3390/app11125360

Abstract

Low-level laser therapy (LLLT) is recognized as an effective medical tool for the treatment of various conditions requiring tissue repair, pain relief, inflammation treatment, and restoration of tissue dysfunction, and its development and research are growing rapidly. However, studies that analyze molecular biology by applying LLLT to osteoclasts are still insufficient to understand the mechanism. In order for LLLT to be suggested as an appropriate treatment method for the treatment of various bone diseases, it is necessary to elucidate the effect and mechanism of LLLT on osteoclast differentiation. In this study, we investigated the effect of LLLT on osteoclast differentiation using murine macrophage (RAW 264.7) cells by means of a Ga-As-Al laser (λ = 810, 80 mW). Our results indicate that LLLT did not induce cytotoxicity in RAW 264.7 cells. When LLLT was applied for 15 s to osteoclasts exposed to RANKL, the expression of NF-κB, ERK, p38, and c-Fos, which are associated with expression of NFATc1, was increased. The RT-PCR results also demonstrated significantly increased expression of osteoclast-specific genes, including NFATc1, TRAP, the calcitonin receptor, and cathepsin K, compared with the control. Taken together, we concluded that low-level laser irradiation induces osteoclastogenesis by enhancing the expression of NF-κB, MAPKs (ERK, p38), c-Fos, and NFATc1 in RAW 264.7 cells. These findings indicate that low-level laser irradiation could be considered a potential treatment option in various metabolic bone diseases that require osteoclastic activity and bone formation.

Highlights

Bone homeostasis is a complex process that is precisely maintained throughout life by a balance between the bone-forming activity of osteoblasts and the bone-resorbing activity of osteoclasts [1,2,3]
The receptor activator of the nuclear factor κB (NF-κB) ligand (RANKL) is a cytokine produced by osteoblasts, which binds to the RANK (NF-κB receptor activator) receptor present in osteoclast progenitor cells
The binding of RANKL and its receptor RANK on the osteoclast induces the recruitment of cytoplasmic tumor necrosis factor receptor-associated factor 6 (TRAF6) activation, and this leads to the activation of downstream molecules, such as NFATc1, NF-κB, mitogen-activated protein kinases (MAPKs), c-Fos, and c-Jun [10,11,12,13]

Summary

Introduction

Bone homeostasis is a complex process that is precisely maintained throughout life by a balance between the bone-forming activity of osteoblasts and the bone-resorbing activity of osteoclasts [1,2,3]. The receptor activator of the nuclear factor κB (NF-κB) ligand (RANKL) is a cytokine produced by osteoblasts, which binds to the RANK (NF-κB receptor activator) receptor present in osteoclast progenitor cells As a result, this leads to the differentiation of osteoclast progenitor cells and the activation of mature osteoclasts [8,9]. The binding of RANKL and its receptor RANK on the osteoclast induces the recruitment of cytoplasmic tumor necrosis factor receptor-associated factor 6 (TRAF6) activation, and this leads to the activation of downstream molecules, such as NFATc1, NF-κB, mitogen-activated protein kinases (MAPKs), c-Fos, and c-Jun [10,11,12,13] These transcription factors induce the complex responses of various genes, allowing the osteoclast progenitor cells to mature into multinuclear osteoclasts [14]. Mature osteoclasts degrade bone matrix proteins and inorganic components of bone by releasing various types of protein, including: Calcitonin receptor, tartrate resistant acid phosphatase (TRAP), cathepsin K, and matrix metalloproteinase-9 (MMP-9) [15,16]

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