Force-Induced Autophagy in Periodontal Ligament Stem Cells Modulates M1 Macrophage Polarization via AKT Signaling

Abstract

Autophagy, a lysosomal degradation pathway, serves as a protective cellular mechanism in maintaining cell and tissue homeostasis under mechanical stimulation. As the mechanosensitive cells, periodontal ligament stem cells (PDLSCs) play an important role in the force-induced inflammatory bone remodeling and tooth movement process. However, whether and how autophagy in PDLSCs influences the inflammatory bone remodeling process under mechanical force stimuli is still unknown. In this study, we found that mechanical force stimuli increased the expression of the autophagy protein LC3, the number of M1 macrophages and osteoclasts, as well as the ratio of M1/M2 macrophages in the compression side of the periodontal ligament in vivo. These biological changes induced by mechanical force were repressed by the application of an autophagy inhibitor 3-methyladenine. Moreover, autophagy was activated in the force-loaded PDLSCs, and force-stimulated PDLSC autophagy further induced M1 macrophage polarization in vitro. The macrophage polarization could be partially blocked by the administration of autophagy inhibitor 3-methyladenine or enhanced by the administration of autophagy activator rapamycin in PDLSCs. Mechanistically, force-induced PDLSC autophagy promoted M1 macrophage polarization via the inhibition of the AKT signaling pathway. These data suggest a novel mechanism that force-stimulated PDLSC autophagy steers macrophages into the M1 phenotype via the AKT signaling pathway, which contributes to the inflammatory bone remodeling and tooth movement process.

Shear Stress Enhances the Paracrine-Mediated Immunoregulatory Function of Human Periodontal Ligament Stem Cells via the ERK Signalling Pathway

“…Recently, our group showed that TLR3 induced the expression IFN-γ-independent IDO, resulting in inhibition of peripheral blood mononuclear cell (PBMC) proliferation and upregulation of a Treg-specific gene marker, forkhead box P3 or FOXP3 [7]. Additionally, mechanical stimuli have also been applied in vitro to regulate immunomodulatory properties of both PDL cells [35,36] and bone marrow-derived MSCs (BM-MSCs) [37] PDL cells are considered as mechanosensory cells that can perceive and respond to mechanical stress driven by mastication, speech or orthodontic movement [38]. Several studies suggested that mechanical stimuli are important factors in regulating periodontal tissue homeostasis [39][40][41].…”

Effect of Tensile Frequency on the Osteogenic Differentiation of Periodontal Ligament Stem Cells

“…The PI3K-Akt signaling pathway has been reported to be involved in the mechanical force-induced osteoblast differentiation of PDLSCs. 41 , 42 The MAPK signaling pathway also have been found to participate in the mechano-transduction of PDLSCs. 43 , 44 …”

Immunomodulatory Activities of Periodontal Ligament Stem Cells in Orthodontic Forces-Induced Inflammatory Processes: Current Views and Future Perspectives

“…He et al [ 32 ] observed increased expression of pro-inflammatory cytokines in in vitro cultured macrophages after adding conditioned medium from hPDLSCs treated with mechanical forces through hydrogen sulfide (H 2 S) production. Jiang et al [ 33 ] also showed increased M1 macrophage polarization after stimulating macrophages with supernatant of hPDLSCs, which were treated with compressive forces for 12 h in vitro . Zhao et al [ 46 ] also demonstrated enhanced in vitro M1 macrophage polarization by adding exosomes secreted from hPDLSCs which were stimulated with static compressive forces for 4 h. It should be noted that these three studies [ 32 , 33 , 46 ] were conducted in the absence of any inflammatory stimuli and this might underlie the promotion of M1 polarization by mechanically treated hPDLSCs.…”

“…Jiang et al [ 33 ] also showed increased M1 macrophage polarization after stimulating macrophages with supernatant of hPDLSCs, which were treated with compressive forces for 12 h in vitro . Zhao et al [ 46 ] also demonstrated enhanced in vitro M1 macrophage polarization by adding exosomes secreted from hPDLSCs which were stimulated with static compressive forces for 4 h. It should be noted that these three studies [ 32 , 33 , 46 ] were conducted in the absence of any inflammatory stimuli and this might underlie the promotion of M1 polarization by mechanically treated hPDLSCs. Most studies imply that hPDLSCs favor M2 anti-inflammatory phenotype; however, this ability is enhanced by the inflammatory environment and in absence of any mechanical forces [ 47 – 50 ], whereas one study [ 47 ] revealed an enhanced polarization to the M1 pro-inflammatory phenotype in the presence of extracellular vesicles derived from lipopolysaccharide-treated hPDLSCs in the absence of mechanical forces.…”

“…This accumulation could be due to the promotion of M1 polarization by hPDLSCs, as we already mentioned above. Jiang et al [ 33 ] observed increased number of M1 macrophages at the compression side of the PDL in a rat model after applying orthodontic forces for 7 days. This increase may be induced due to enhanced autophagy of hPDLSCs, induced by applied mechanical forces.…”