IL-17A and shear stress modulate osteoclastogenesis/osteogenesis in bone cells

Abstract

Objectives: The molecular mechanisms of bone remodeling under mechanical loading are critical to better understand the metabolism of alveolar bone. Interleukin (IL)-17 is crucial to osteoclast differentiation and activation. This study investigated the regulatory mechanisms of IL-17A (one of the six IL-17 family members) in bone remodeling under shear stress in vitro. Methods: MC3T3-E1 osteoblasts, MLO-A5 post-osteoblasts and MLO-Y4 osteocytes cell lines were stimulated with exogenous IL-17A, respectively. The antibody for IL-17A receptor was used for blocking assays. Bone cells were loaded with flow shear stress and then cultured with or without IL-17A. The expression of osteogenic factors (e.g. runt-related transcription factor 2, collagen-1, alkaline phosphatase, osteocalcin and osteoprotegerin) and osteoclastic factors (e.g. receptor activator of nuclear factor κ-B ligand - RANKL and tumor necrosis factor-α) was analyzed. Bone remodeling pathways of extracellular signal-regulated kinases (ERK), signal transducer and activator of transcription (STAT3) and Eph-ephrin signaling were investigated. Mineralization was determined with MC3T3-E1 and MLO-A5, while osteoclast formation was examined using direct/indirect co-culture of osteoclast precursor bone marrow-derived macrophage cells (BMMs) and MC3T3-E1 or MLO-Y4. Results: IL-17A downregulated osteogenic factors and upregulated osteoclastic factors in bone cells. Additionally, IL-17A inhibited mineralized nodule formation of osteoblasts, while enhanced the osteoclastic differentiation in direct co-culture of MLO-Y4 and BMMs. The above regulation was weakened by antibodies of IL-17A receptor. Moreover, shear stress stimulation could attenuate the role of IL-17A in osteoclastogenesis. Furthermore, ERK, STAT3 and Eph-ephrin signaling pathways were regulated by IL-17A and shear stress. Conclusions: IL-17A promoted osteoclastogenesis and inhibited osteogenisis, which could be regulated by shear stress. ERK, STAT3 and Eph-ephrin signaling play an important role in bone remodeling caused by IL-17A and shear stress.