Repeated stimulation by LPS promotes the senescence of DPSCs via TLR4/MyD88-NF-κB-p53/p21 signaling

Abstract

Dental pulp stem cells (DPSCs), one type of mesenchymal stem cells, are considered to be a type of tool cells for regenerative medicine and tissue engineering. Our previous studies found that the stimulation with lipopolysaccharide (LPS) might introduce senescence of DPSCs, and this senescence would have a positive correlation with the concentration of LPS. The β-galactosidase (SA-β-gal) staining was used to evaluate the senescence of DPSCs and immunofluorescence to show the morphology of DPSCs. Our findings suggested that the activity of SA-β-gal has increased after repeated stimulation with LPS and the morphology of DPSCs has changed with the stimulation with LPS. We also found that LPS bound to the Toll-like receptor 4 (TLR4)/myeloid differentiation factor (MyD) 88 signaling pathway. Protein and mRNA expression of TLR4, MyD88 were enhanced in DPSCs with LPS stimulation, resulting in the activation of nuclear factor-κB (NF-κB) signaling, which exhibited the expression of p65 improved in the nucleus while the decreasing of IκB-α. Simultaneously, the expression of p53 and p21, the downstream proteins of the NF-κB signaling, has increased. In summary, DPSCs tend to undergo senescence after repeated stimulation in an inflammatory microenvironment. Ultimately, these findings may lead to a new direction for cell-based therapy in oral diseases and other regenerative medicines.

Senescence and Host–Pathogen Interactions

“…Strategies may include inducing senescence indirectly via persistent inflammatory responses [23]. For example, pathogen-associated molecular pattern (PAMP) molecules, such as bacterial lipopolysaccharide, have been shown to induce stem cell senescence by the persistent activation of the pattern recognition receptor Toll-like receptor 4 through the NFκB-p53-p21 signalling axis [87]. While it remains unclear whether bacteria exploit PAMPs as an indirect means to hijack inflammation-mediated senescence, dedicated microbial genotoxins are becoming increasingly implicated in direct induction of senescence.…”

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

“…initiates innate immune responses mediated by TLR-4/ MyD88-NF-kB-p53/p21 signaling. 100 Thus, LPS is usually topically administered to mimic pulp inflammation caused by cariogenic microorganisms to some degree; it can cause experimental pulpitis by inducing the production of NO and many other inflammatory cytokines. 3,57,[101][102][103][104] Notably, proinflammatory mediator production is likely to be activated directly by LPS and/or to be related to NO synthesis.…”

Releasing Behavior of Lipopolysaccharide from Gelatin Modulates Inflammation, Cellular Senescence, and Bone Formation in Critical-Sized Bone Defects in Rat Calvaria

“…Residual LPS could be found only in defects treated with the LS-G. Repeated [16] or long-term [45] stimulation by LPS causes cellular senescence in vitro. These results may suggest that it is not extracellular reactive oxygen or inflammatory cytokines, but residual LPS that directly promotes cellular senescence.…”

“…Various stresses, such as oxidative stress and inflammatory cytokines, irreversibly arrest the cell cycle, thereby generating stress-induced senescent cells both in vivo and in vitro [13]. LPS can induce DNA damage [14] and generate stress-induced primary senescent cells in vitro [15,16]. However, information regarding the LPS induction of senescent cells in vivo is still lacking.…”