Micro-Vibration Stimulation Promotes M2 Polarization of Macrophages Beneficial for Osteogenesis Via Activating FAK/P38MAPK and Suppressing Ca <sup>2+</sup>/ERK/ p65NF-κB Signaling Pathways

Abstract

The emergence of osteoimmunology has demonstrated that bone system is closely related to immune system. However, most studies have investigated the interaction between immune cells and bone-related cells under a static cell culture, the effects of mechanical stimuli on the inflammatory responses of macrophages remain elusive. In this work, micro-vibration stimulation (MVS) was introduced into regulating macrophage polarization and functional status. The results found that MVS with 40 Hz in frequency and 0.3 g in magnitude could significantly raise the fraction of CD206-positive M2 population, up-regulate the expression of M2 marker genes, and enhance the secretion of M2 marker proteins in RAW 264.7 macrophages. It suggested that calcium ion and focal adhesion played an important role in transmitting MVS signal. Further inhibitor studies and western blotting analyses indicated that MVS-induced M2 polarization might be attributed to the activation of p38MAPK signaling and suppression of the ERK1/2 and p65NF-κB signaling. Moreover, MVS-mediated macrophage secretion enhanced osteoblastic differentiation of MC3T3-E1 pre-osteoblasts via Wnt/β-catenin and ERK1/2 signaling in a paracrine way. These findings highlight a critical role of MVS in inducing M2 polarization of macrophage to create a pro-osteogenic environment, which offers a drug-free modulatory strategy to regulate immune response and promote osteogenesis.