Background Mitochondrial DNA (mtDNA) is a vital driver of inflammation when it leaks from damaged mitochondria into the cytosol. mtDNA stress may contribute to cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway activation in infectious diseases. Odontoblasts are the first cells challenged by cariogenic bacteria and involved in maintenance of the pulp immune and inflammatory responses to dentine-invading pathogens. In this study, we investigated that mtDNA as an important inflammatory driver participated in defending against bacterial invasion via cGAS-STING pathway in odontoblasts. Methods The normal tissues, caries tissues and pulpitis tissues were measured by western blotting and immunohistochemical staining. Pulpitis model was built in vitro to evaluated the effect of the cGAS-STING pathway in odontoblast-like cell line (mDPC6T) under inflammation. Western blot and real-time PCR were performed to detect the expression of cGAS-STING pathway and pro-inflammatory cytokines. The mitochondrial function was evaluated reactive oxygen species (ROS) generated by mitochondria using MitoSOX Red dye staining. Cytosolic DNA was assessed by immunofluorescent staining and real-time PCR in mDPC6T cells after LPS stimulation. Furthermore, mDPC6T cells were treated with ethidium bromide (EtBr) to deplete mtDNA or transfected with isolated mtDNA. The expression of cGAS-STING pathway and pro-inflammatory cytokines were measured. Results The high expression of cGAS and STING in caries and pulpitis tissues in patients, which was associated with inflammatory progression. The cGAS-STING pathway was activated in inflamed mDPC6T. STING knockdown inhibited the nuclear import of p65 and IRF3 and restricted the secretion of the inflammatory cytokines CXCL10 and IL-6 induced by LPS. LPS caused mitochondrial damage in mDPC6T, which promoted mtDNA leakage into the cytosol. Depletion of mtDNA inhibited the cGAS-STING pathway and nuclear translocation of p65 and IRF3. Moreover, repletion of mtDNA rescued the inflammatory response, which was inhibited by STING knockdown. Conclusion Our study systematically identified a novel mechanism of LPS-induced odontoblast inflammation, which involved mtDNA leakage from damaged mitochondria into the cytosol stimulating the cGAS-STING pathway and the inflammatory cytokines IL-6 and CXCL10 secretion. The mtDNA-cGAS-STING axis could be a potent therapeutic target to prevent severe bacterial inflammation in pulpitis. Graphic abstract
Alleviating odontoblast inflammation is crucial to control the progression of pulpitis. Mitochondrial DNA (mtDNA) is a vital driver of inflammation when it leaks from mitochondria of inflamed odontoblasts into the cytosol. Bacteria-induced inflammation leads to a novel type of cell death named pyroptosis. The canonical pyroptosis is a gasdermin (GSDM)-dependent cytolytic programmed cell death characterized by cell swelling and pore formation in the plasma membrane. To date, whether odontoblast cytosolic mtDNA regulates dental pulp inflammation through the canonical pyroptosis pathway remains to be elucidated. In this study, high gasdermin D (GSDMD) expression was detected in human pulpitis. We found that LPS stimulation of mDPC6T cells promoted BAX translocation from the cytosol to the mitochondrial membrane, leading to mtDNA release. Moreover, overexpression of isolated mtDNA induced death in a large number of mDPC6T cells, which had the typical appearance of pyroptotic cells. Secretion of the inflammatory cytokines CXCL10 and IFN-β was also induced by mtDNA. These results suggest that cytosolic mtDNA participates in the regulation of odontoblast inflammation through GSDMD-mediated pyroptosis in vitro. Interestingly, after overexpression of mtDNA, the expression of inflammatory cytokines CXCL10 and IFN-β was increased and not decreased in GSDMD knockdown mDPC6T cells. We further proposed a novel model in which STING-dependent inflammation in odontoblast-like cell is a compensatory mechanism to control GSDMD-mediated pyroptosis, jointly promoting the immune inflammatory response of odontoblasts. Collectively, these findings provide the first demonstration of the role of the mtDNA-GSDMD-STING in controlling odontoblast inflammation and a detailed description of the underlying interconnected relationship.
Mitochondrial transfer is emerging as a promising therapeutic strategy for tissue repair, but whether it protects against pulpitis remains unclear. Here, we show that hyperactivated nucleotide‐binding domain and leucine‐rich repeat protein3 (NLRP3) inflammasomes with pyroptotic cell death was present in pulpitis tissues, especially in the odontoblast layer, and mitochondrial oxidative stress (OS) was involved in driving this NLRP3 inflammasome‐induced pathology. Using bone marrow mesenchymal stem cells (BMSCs) as mitochondrial donor cells, we demonstrated that BMSCs could donate their mitochondria to odontoblasts via tunnelling nanotubes (TNTs) and, thus, reduce mitochondrial OS and the consequent NLRP3 inflammasome‐induced pyroptosis in odontoblasts. These protective effects of BMSCs were mostly blocked by inhibitors of the mitochondrial function or TNT formation. In terms of the mechanism of action, TNF‐α secreted from pyroptotic odontoblasts activates NF‐κB signalling in BMSCs via the paracrine pathway, thereby promoting the TNT formation in BMSCs and enhancing mitochondrial transfer efficiency. Inhibitions of NF‐κB signalling and TNF‐α secretion in BMSCs suppressed their mitochondrial donation capacity and TNT formation. Collectively, these findings demonstrated that TNT‐mediated mitochondrial transfer is a potential protective mechanism of BMSCs under stress conditions, suggesting a new therapeutic strategy of mitochondrial transfer for dental pulp repair.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.