Dual role of autophagy in lipopolysaccharide-induced preodontoblastic cells

Mitochondrial homeostasis in odontoblast: Physiology, pathogenesis and targeting strategies

Caries and pulpitis remain a major global disease burden and affect the quality of life of patients. Odontoblasts are key players in the progression of caries and pulpitis, not only secreting and mineralizing to form dentin, but also acting as a wall of defense to initiate immune defenses. Mitochondrion is an information processor for numerous cellular activities, and dysregulation of mitochondrion homeostasis not only affects cellular metabolism but also triggers a wide range of diseases. Elucidating mitochondrial homeostasis in odontoblasts can help deepen scholars' understanding of odontoblast-associated diseases. Articles on mitochondrial homeostasis in odontoblasts were evaluated for information pertinent to include in this narrative review. This narrative review focused on understanding the complex interplay between mitochondrial homeostasis in odontoblasts under physiological and pathological conditions. Furthermore, mitochondria-centered therapeutic strategies (including mitochondrial base editing, targeting platforms, and mitochondrial transplantation) were emphasized by resolving key genes that regulate mitochondrial function. Mitochondria are involved in odontoblast differentiation and function, and act as mitochondrial danger-associated molecular patterns (mtDAMPs) to mediate odontoblast pathological progression. Novel mitochondria-centered therapeutic strategies are particularly attractive as emerging therapeutic approaches for the maintenance of mitochondrial homeostasis. It is expected to probe key events of odontoblast differentiation and advance the clinical resolution of dentin formation and mineralization disorders and odontoblast-related diseases.

Autophagy, a double-edged sword for oral tissue regeneration

BACKGROUND

Oral health is of fundamental importance to maintain systemic health in humans. Stem cell-based oral tissue regeneration is a promising strategy to achieve the recovery of impaired oral tissue. As a highly conserved process of lysosomal degradation, autophagy induction regulates stem cell function physiologically and pathologically. Autophagy activation can serve as a cytoprotective mechanism in stressful environments, while insufficient or over-activation may also lead to cell function dysregulation and cell death.

AIM OF REVIEW

This review focuses on the effects of autophagy on stem cell function and oral tissue regeneration, with particular emphasis on diverse roles of autophagy in different oral tissues, including periodontal tissue, bone tissue, dentin pulp tissue, oral mucosa, salivary gland, maxillofacial muscle, temporomandibular joint, etc. Additionally, this review introduces the molecular mechanisms involved in autophagy during the regeneration of different parts of oral tissue, and how autophagy can be regulated by small molecule drugs, biomaterials, exosomes/RNAs or other specific treatments. Finally, this review discusses new perspectives for autophagy manipulation and oral tissue regeneration.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Overall, this review emphasizes the contribution of autophagy to oral tissue regeneration and highlights the possible approaches for regulating autophagy to promote the regeneration of human oral tissue.

The role of autophagy in odontogenesis, dental implant surgery, periapical and periodontal diseases

Autophagy is a cellular process that is evolutionarily conserved, involving the sequestration of damaged organelles and proteins into autophagic vesicles, which subsequently fuse with lysosomes for degradation. Autophagy controls the development of many diseases by influencing apoptosis, inflammation, the immune response and different cellular processes. Autophagy plays a significant role in the aetiology of disorders associated with dentistry. Autophagy controls odontogenesis. Furthermore, it is implicated in the pathophysiology of pulpitis and periapical disorders. It enhances the survival, penetration and colonization of periodontal pathogenic bacteria into the host periodontal tissues and facilitates their escape from host defences. Autophagy plays a crucial role in mitigating exaggerated inflammatory reactions within the host's system during instances of infection and inflammation. Autophagy also plays a role in the relationship between periodontal disease and systemic diseases. Autophagy promotes wound healing and may enhance implant osseointegration. This study reviews autophagy's dento-alveolar effects, focusing on its role in odontogenesis, periapical diseases, periodontal diseases and dental implant surgery, providing valuable insights for dentists on tooth development and dental applications. A thorough examination of autophagy has the potential to discover novel and efficacious treatment targets within the field of dentistry.

Fusobacterium nucleatum exacerbates the progression of pulpitis by regulating the STING-dependent pathway

Bacterial infection is the main cause of pulpitis. However, whether a dominant bacteria can promote the progression of pulpitis and its underlying mechanism remains unclear. We provided a comprehensive assessment of the microbiota alteration in pulpitis using 16S rRNA sequencing. Fusobacterium nucleatum was the most enriched in pulpitis and played a pathogenic role accelerating pulpitis progression in rat pulpitis model. After odontoblast-like cells cocultured with F. nucleatum, the stimulator of interferon genes (STING) pathway and autophagy were activation. There was a float of STING expression during F. nucleatum stimulation. STING was degraded by autophagy at the early stage. At the late stage, F. nucleatum stimulated mitochondrial Reactive Oxygen Species (ROS) production, mitochondrial dysfunction and then mtDNA escape into cytosol. mtDNA, which escaped into cytosol, caused more cytosolic mtDNA binds to cyclic GMP-AMP synthase (cGAS). The release of IFN-β was dramatically reduced when mtDNA-cGAS-STING pathway inhibited. STING-/- mice showed milder periapical bone loss and lower serum IFN-β levels compared with wildtype mice after 28 days F. nucleatum-infected pulpitis model establishment. Our data demonstrated that F. nucleatum exacerbated the progression of pulpitis, which was mediated by the STING-dependent pathway.

Ciliary Neurotrophic Factor (CNTF) Inhibits In Vitro Cementoblast Mineralization and Induces Autophagy, in Part by STAT3/ERK Commitment

In animal models, the administration of ciliary neurotrophic factor (CNTF) was demonstrated to reduce bone mass and to participate in bone remodeling. Cementoblasts, a cell type embedded in the cementum, are the main cells to produce and mineralize the extracellular matrix. The effect of CNTF on cementoblasts has not yet been addressed. Thus, the goal of this in vitro study was to investigate possible influences of exogenous CNTF on cementogenesis, as well as autophagy regulation and subsequent mechanisms in cementoblasts. Cementoblasts (OCCM-30) were stimulated with exogenous CNTF. Alizarin Red staining was performed to analyze the functional differentiation (mineralization) of OCCM-30 cells. The release of OPG was quantified by ELISA. The expression of cementogenesis markers (RUNX-2, OCN, BMP-7, BSP, and SPON-2) was evaluated by RT-qPCR. Western blotting (WB) was performed for the protein expression of STAT3, COX-2, SHP-2, cPLAα, cPLAβ; ERK1/2, P38, and JNK. The autophagic flux was assessed using WB and RT-qPCR analysis of LC3A/B, Beclin-1, and Atg-5, and the autophagosome was investigated by immunofluorescence staining (IF). The ERK1/2 (FR180204) or STAT3 (sc-202818) antagonist was added, and the cellular response was analyzed using flow cytometry. Exogenous CNTF significantly attenuated mineralized nodule formation, impaired OPG release, and downregulated the mRNA levels of RUNX-2, OCN, BMP-7, and BSP. Moreover, CNTF induced the phosphorylation of STAT3 and activated a transient activation of SHP-2, cPLAβ, ERK1/2, P38, and JNK protein. CNTF also induced autophagosome formation and promoted autophagy-associated gene and protein expressions. Additionally, the inhibition of ERK1/2 or STAT3 reversed a CNTF-induced mineralization impairment and had regulatory effects on CNTF-induced autophagosome formation. Our data revealed that CNTF acts as a potent inhibitor of cementogenesis, and it can trigger autophagy, in part by ERK1/2 and STAT3 commitment in the cementoblasts. Thus, it may play an important role in inducing or facilitating inflammatory root resorption during orthodontic tooth movement.

The molecular regulation of autophagy in antimicrobial immunity

Autophagy is a catabolic process that can degrade worn-out organelles and invading pathogens. The activation of autophagy regulates innate and adaptive immunity, playing a key role in the response to microbial invasion. Microbial infection may cause different consequences such as the elimination of invaders through autophagy or xenophagy, host cell death, and symbiotic relationships. Pathogens adapt to the autophagy mechanism and further relieve intracellular stress, which is conducive to host cell survival and microbial growth. The regulation of autophagy forms a complex network through which host immunity is modulated, resulting in a variety of pathophysiological manifestations. Modification of the autophagic pathway is an essential target for the development of antimicrobial drugs.

A20 alleviated caspase-1-mediated pyroptosis and inflammation stimulated by Porphyromonas gingivalis lipopolysaccharide and nicotine through autophagy enhancement

Periodontitis is the leading cause of tooth loss, and patients with smoking habits are at an increased risk of developing periodontitis. A20 (the tumor necrosis factor alpha-induced protein 3, TNFAIP3) is one of the key regulators of inflammation and cell death in numerous tissues. Emerging researches indicated A20 as a fundamental molecule in the periodontal tissue. This study was to evaluate the role of A20 against cell death and inflammation in periodontitis and to elucidate the underlying mechanisms. In our study, western blot, autophagy detection, and transmission electron microscopy showed that lipopolysaccharide from Porphyromonas gingivalis (Pg.LPS) and nicotine (NI) could enhance the activation of autophagy. Pg.LPS and NI induce the pyroptosis of human periodontal ligament cells (hPDLCs), as evidenced by the decrease of membrane integrity and the increase of NLRP3, GSDMD, GSDMD-N, caspase-1 activity, and the pro-inflammatory cytokines of IL-1β, IL-6, TNF-α. Further researches were focused on that A20, an ubiquitin-editing enzyme, was linked to hPDLCs pyroptosis. Overexpression or silencing A20 could diminish or aggravate pyroptosis in hPDLCs by the modulation of autophagy. The above results demonstrated that A20 dictated the cross-talk between pyroptosis and autophagy. Overexpression of A20 enhanced autophagy to reduce pyroptosis, and thus alleviating inflammation, suggesting that A20 may be a potent target in the treatment of periodontitis.

Autophagy in aging-related oral diseases

Autophagy is an intracellular degradation mechanism that allows recycling of organelles and macromolecules. Autophagic function increases metabolite availability modulating metabolic pathways, differentiation and cell survival. The oral environment is composed of several structures, including mineralized and soft tissues, which are formed by complex interactions between epithelial and mesenchymal cells. With aging, increased prevalence of oral diseases such as periodontitis, oral cancer and periapical lesions are observed in humans. These aging-related oral diseases are chronic conditions that alter the epithelial-mesenchymal homeostasis, disrupting the oral tissue architecture affecting the quality of life of the patients. Given that autophagy levels are reduced with age, the purpose of this review is to discuss the link between autophagy and age-related oral diseases.

Epigenetic Control of Autophagy Related Genes Transcription in Pulpitis via JMJD3

Autophagy is an intracellular self-cannibalization process delivering cytoplasmic components to lysosomes for digestion. Autophagy has been reported to be involved in pulpitis, but the regulation of autophagy during pulpitis progression is largely unknown. To figure out the epigenetic regulation of autophagy during pulpitis, we screened several groups of histone methyltransferases and demethylases in response to TNFα treatment. It was found JMJD3, a histone demethylase reducing di- and tri-methylation of H3K27, regulated the expression of several key autophagy genes via demethylation of H3K27me3 at the gene promoters. Our study highlighted the epigenetic regulation of autophagy genes during pulpitis, which will potentially provide a novel therapeutic strategy.

Proliferation of Lung Epithelial Cells Is Regulated by the Mechanisms of Autophagy Upon Exposure of Soots

Background

Soots are known to cause many diseases in humans, but their underlying mechanisms of toxicity are still not known. Here, we report that soots induce cell proliferation of lung epithelial cells via modulating autophagy pathways.

Results

Fullerene soot and diesel exhaust particles (DEP) induced cell proliferation of lung epithelial, A549 cells via distinct autophagic mechanisms and did not cause cell death. Exposure of fullerene soot protected the cell death of A549 cells, caused by hydrogen peroxide, and inhibited LPS-induced autophagy. Fullerene soot co-localized with the autophagic proteins and inhibited starvation-induced autophagy (downregulated ATG-5, beclin-1, p62, and LC3 expressions) independent of its antioxidant properties. Similarly, it decreased the expression profile of autophagic genes and upregulated the proliferation-responsive gene, Ki-67, in mice. We observed that expressions of fullerene soot-responsive genes (Beclin-1, ATG-5, and p62) were reverted by Akt Inhibitor X, indicating an important role of the Akt pathway. At an elemental level, we found that elemental carbon of fullerene soot may be converted into organic carbon, as measured by OCEC, which may point fullerene soot as a source of carbon. On the other hand, DEP upregulated the expressions of autophagy genes. Akt Inhibitor X did not attenuate DEP-induced cell proliferation and autophagic response. However, an autophagic inhibitor, chloroquine, and significantly inhibited DEP-induced cell proliferation.

Conclusion

It can be said that distinct autophagic mechanisms are operational in cell proliferation of lung epithelial cells due to soots, which may be responsible for different diseases. Understanding the mechanism of these pathways provides some important targets, which can be utilized for the development of future therapeutics.

Autophagy in tooth: Physiology, disease and therapeutic implication

Autophagy is an evolutionarily conserved cellular process, in which damaged organelles and proteins are engulfed in autophagic vesicles and subsequently fuse with lysosomes for degradation. Autophagy is widely involved in different physiologic or pathologic processes in human. Accumulating evidence indicates that autophagy operates as a critical quality control mechanism to maintain pulp homeostasis and structural integrity of the dentin-pulp complex. Autophagy is activated during stresses and is involved in the pathogenesis of pulpitis and periapical infection. Recent discoveries have also provided intriguing insights into the roles of autophagy in tooth development, pulp aging and stress adaptation. In this review, we provide an update on the multifaceted functions of autophagy in physiology and pathophysiology of tooth. We also discuss the therapeutic implications of autophagy modulation in diseases and the regeneration of dentin-pulp complex.

Midkine Promotes Odontoblast-like Differentiation and Tertiary Dentin Formation

Autophagy is an intracellular self-degradation process that is essential for tissue development, cell differentiation, and survival. Nevertheless, the role of autophagy in tooth development has not been definitively identified. The goal of this study was to investigate how autophagy is involved in midkine (MK)-mediated odontoblast-like differentiation, mineralization, and tertiary dentin formation in a mouse tooth pulp exposure model. In vitro studies show that MK and LC3 have similar expression patterns during odontoblast-like cell differentiation. Odontoblast-like cell differentiation is promoted through MK-mediated autophagy, which leads to increased mineralized nodule formation. Subcutaneous transplantation of hydroxyapatite/tricalcium phosphate with rMK-treated human dental pulp cells led to dentin pulp-like tissue formation through MK-mediated autophagy. Furthermore, MK-mediated autophagy induces differentiation of dental pulp cells into odontoblast-like cells that form DSP-positive tertiary dentin in vivo. Our findings may provide 1) novel insight into the role of MK in regulating odontoblast-like differentiation and dentin formation in particular via autophagy and 2) potential application of MK in vital pulp therapy.

Induction of autophagy protects human dental pulp cells from lipopolysaccharide-induced pyroptotic cell death

The NOD-like receptor protein 3/caspase-1 inflammasome can be activated in human dental pulp tissue and fibroblasts; however, the underlying mechanisms are poorly understood. In the present study, lipopolysaccharide (LPS) was used to treat dental pulp cells to establish an inflammation model. Cell viability was examined by sulforhodamine B assay. Interleukin (IL)-1β, caspase-1, microtubule-associated protein-1 light chain 3-II/I and p62 were determined by western blotting and ELISA. The phosphorylation (p-) levels of NF-κB and NF-κB inhibitor (IκB)α protein were observed by western blotting. The results demonstrated that LPS induced pyroptotic cell death in cultured dental pulp cells, which was supported by the increased levels of IL-1β, IL-18 and caspase-1. Rapamycin and 3-methyladenine (3-MA) were used to activate and inhibit autophagy, and it was observed that LPS increased autophagy and rapamycin reduced LPS-induced dental pulp cell pyroptosis. However, 3-MA aggravated LPS-induced dental pulp cell pyroptosis. In addition, LPS inhibited the expression of IκBα, but increased the expression of p-NF-κB. Compared with the LPS group, 3-MA further inhibited the expression of IκBα but promoted the expression of p-NF-κB. However, rapamycin produced the opposite results to LPS. Under LPS treatment, the NF-κB pathway inhibitor BAY11-7082 further enhanced the inhibitory effects of rapamycin, but inhibited the promoting effects of 3-MA on the protein expression levels of IL-1β and caspase-1. The results of the present study demonstrated that there is an important crosstalk between autophagy, pyroptosis and the NF-κB pathway, and that the modulation of pyroptosis in dental pulp cells may be a promising strategy to pulpitis therapy.

Post-mitotic odontoblasts in health, disease, and regeneration

OBJECTIVE

Description of the odontoblast lifecycle, an overview of the known complex molecular interactions that occur when the health of the dental pulp is challenged and the current and future management strategies on vital and non-vital teeth.

METHODS

A literature search of the electronic databases included MEDLINE (1966-April 2019), CINAHL (1982-April 2019), EMBASE and EMBASE Classic (1947-April 2019), and hand searches of references retrieved were undertaken using the following MESH terms 'odontoblast*', 'inflammation', 'dental pulp*', 'wound healing' and 'regenerative medicine'.

RESULTS

Odontoblasts have a sensory and mechano-transduction role so as to detect external stimuli that challenge the dental pulp. On detection, odontoblasts stimulate the innate immunity by activating defence mechanisms key in the healing and repair mechanisms of the tooth. A better understanding of the role of odontoblasts within the dental pulp complex will allow an opportunity for biological management to remove the cause of the insult to the dental pulp, modulate the inflammatory process, and promote the healing and repair capabilities of the tooth. Current strategies include use of conventional dental pulp medicaments while newer methods include bioactive molecules, epigenetic modifications and tissue engineering.

CONCLUSION

Regenerative medicine methods are in their infancy and experimental stages at best. This review highlights the future direction of dental caries management and consequently research.

Odontoblastic Exosomes Attenuate Apoptosis in Neighboring Cells

Each odontoblast is tightly linked to other odontoblasts. They form a line of defense and are capable of withstanding external stimuli, particularly the inflammation caused by caries. Thus, we investigated exosomes derived from odontoblasts as an intercellular mechanism by which inflamed odontoblasts are protected from apoptosis. CD63, an exosome marker, was expressed at high levels in caries-affected regions of the dental pulp. We conducted an ex vivo experiment by applying different concentrations of lipopolysaccharide (LPS) to the odontoblast-like cells (mineralization was induced in stem cells derived from the apical papilla). Odontoblast-like cells treated with a high concentration of LPS (20 µg/mL LPS, severely affected) exhibited an accelerated release of exosomes, which attenuated the LPS-induced cell apoptosis of odontoblast-like cells treated with a low concentration of LPS (1 µg/mL LPS, mildly affected). Next, we blocked exosome uptake with chlorpromazine, and the rescue effect vanished. Based on our findings, severely inflamed odontoblasts attenuate the apoptosis of mildly inflamed neighboring cells through an exosome-mediated intercellular signaling pathway.

Lipopolysaccharide-induced DNA damage response activates nuclear factor κB signalling pathway via GATA4 in dental pulp cells

AIM

To investigate the role of GATA-binding protein 4 (GATA4) in the inflammatory response induced by DNA double-strand breaks (DSBs) in human dental pulp cells (hDPCs).

METHODOLOGY

Lipopolysaccharide (LPS) was used for stimulating inflammation in dental pulp tissue in vivo and hDPCs in vitro. Expression levels of GATA4 and γ-H2A.X (a marker for DSBs) were detected at different stages of pulpitis in a rat model and human pulp tissues by immunohistochemistry. Real-time quantitative polymerase chain reaction and Western blot were performed to assess expression of GATA4 and γ-H2A.X and the activation of nuclear factor κB (NF-κB) in hDPCs stimulated by LPS. The comet assay was used for detecting the extent of DSBs in hDPCs. Immunocytochemistry and Western blot were utilized to evaluate expression of γ-H2A.X and GATA4 and activation of NF-κB in hDPCs pre-treated with inhibitors of DNA damage response or transfected with GATA4 small interfering RNA before the treatment of LPS. Data were analysed statistically using one-way anova or Kruskal-Wallis tests.

RESULTS

The expression of GATA4 and activation of DNA damage response and NF-κB in inflamed pulp tissue and LPS-treated hDPCs were identified. Significantly decreased expression of GATA4 and significantly decreased inflammatory processes in hDPCs were demonstrated via suppression of DNA damage response (P < 0.05). In GATA4-knockdown cells, the expression of γ-H2A.X did not change, but nuclear translocation of p65 was significantly suppressed (P < 0.05) upon induction by LPS.

CONCLUSIONS

Lipopolysaccharide-induced DSBs activated the NF-κB signalling pathway in hDPCs, and GATA4 acts as a positive moderator of the progress. The involvement of GATA4 in this pathology may serve as a therapeutic target in pulpitis.

Lipopolysaccharide promotes lung fibroblast proliferation through autophagy inhibition via activation of the PI3K-Akt-mTOR pathway

Pulmonary fibrosis is a major cause of death in patients with acute respiratory distress syndrome (ARDS). Our previous study revealed that lipopolysaccharide (LPS) challenge could lead to mouse lung fibroblast proliferation. Additionally, inhibition of autophagy in lung fibroblasts was also reported to be crucial during the process of pulmonary fibrosis. However, the correlation between proliferation and inhibition of autophagy of lung fibroblasts and the underlying mechanism remain unknown. In this study, we report that autophagy was inhibited in mouse lung fibroblasts after LPS challenge, and was accompanied by activation of the PI3K-Akt-mTOR signaling pathway. Treating mouse lung fibroblasts with LPS resulted in mTOR and Akt phosphorylation, p62 up-regulation, and significant down-regulation of autophagosomes, which could be reversed by PI3K-Akt inhibitors (Ly294002) or mTOR inhibitors (rapamycin, RAPA). Furthermore, either LPS or hydroxychloroquine (HCQ), an autophagy inhibitor, could promote mouse lung fibroblast proliferation, which could be reversed by RAPA application. The present research therefore reveals that LPS promotes lung fibroblast proliferation through autophagy inhibition via activation of the PI3K-Akt-mTOR pathway.

Expression of autophagy‑associated proteins in rat dental irreversible pulpitis

Autophagy serves an important role in numerous diseases, as well as in infection and inflammation. Irreversible pulpitis (IP) is one of the most common inflammatory endodontic diseases, and autophagy has been reported to regulate IP in vitro. However, the level of autophagy in the IP pathogenic process in vivo remains unknown. The aim of the current study was, thus, to investigate the levels of autophagy-associated proteins in rats with IP in vivo. A rat dental IP model was successfully constructed, and five different time points (0, 1, 3, 5 and 7 days) were investigated. The levels of the autophagy-related 5 (ATG5), ATG7, light chain 3 (LC3) and Beclin-1 proteins exhibited a time-dependent increase in rats with IP, whereas the levels of mammalian target of rapamycin and p62/sequestosome 1 were decreased. In addition, the levels of ATG proteins were specifically increased in odontoblasts and microvascular endothelial cells in pulpitis tissue. Based on these findings, autophagy may serve an important role in IP, and the present study data provide a new insight into the IP pathogenesis and treatment.

Zika virus induces abnormal cranial osteogenesis by negatively affecting cranial neural crest development

Zika virus (ZIKV) infection during gestation is deemed to be coupled to birth defects through direct impairment of the nervous system during neurogenesis. However, in this study, our data showed that ZIKV infection dramatically suppressed cranial osteogenesis, shown by Safranin O/Fast Green and alizarin red staining, in chick embryos, which provides another possibility that craniofacial bone malformation caused by ZIKV may be a major cause of ZIKV-mediated birth defects. By immunofluorescent staining and electron microcopy, we confirmed ZIKV infection in chick embryo neural tubes and sites of neural crest. Next, in vivo (chick embryos) and in vitro [primary culture of neural crest cells (NCC)] ZIKV and HNK-1 double immunofluorescent staining demonstrated that ZIKV infection inhibited the production of migratory NCC. The reduction of both AP-2α- and Pax7-positive NCC in HH10 chick embryos infected by ZIKV confirmed that abnormal development of cranial NCC also occurred in the migratory process. Whole mount in situ hybridization demonstrated that cadherin 6B expression was elevated and Slug, FoxD3, and BMP4/Msx1 expressions decreased in ZIKV-infected HH10 chick embryos, implying that epithelial-mesenchymal transition (EMT) of neural crest production was blocked by ZIKV infection. Moreover, in vivo and in vitro pHIS3 and Pax7 double immunofluorescent staining showed that NCC proliferation was repressed by ZIKV infection. C-caspase-3 and AP-2α double immunofluorescent staining in HH10 chick embryos and western blotting showed that NCC apoptosis increased following ZIKV infection. Finally, electron microscopy showed multiple autophagosomes in ZIKV-infected embryos, and western blot and LC3B immunofluorescent staining demonstrated that autophagy-related genes were activated by ZIKV infection. Taken together, our data first showed that ZIKV infection during embryogenesis could interfere with cranial neural crest development, which in turn causes aberrant cranial osteogenesis. Our results provided new insights into brain malformations induced by ZIKV infection.

The synergistic effect of NOD2 and TLR4 on the activation of autophagy in human submandibular gland inflammation

BACKGROUND

Sialadenitis is a nonneoplastic disease that causes salivary dysfunction. Autophagy may be involved in helping protect salivary function when the salivary gland is impaired; this process is primarily activated by sensors of innate immunity, such as Toll-like receptors and nucleotide-binding oligomerization domain (NOD)-like receptors. The role of these pattern recognition receptors (PRRs) in the regulation of salivary gland tissue defense and homeostasis has been underappreciated. This study hypothesized that NOD2 and TLR4 have a synergistic effect on the activation of autophagy in human submandibular gland (HSG) inflammation.

METHODS

Submandibular gland inflammation was modeled by treating HSG cell lines in vitro with muramyl dipeptide (MDP) and lipopolysaccharide (LPS) for 24 hours. The mRNA and protein expression of NOD2, TLR4 and autophagy-related proteins (ATG5, LC3, Beclin1) were evaluated by real-time PCR and Western blot. Immunohistochemistry and double immunofluorescence were used to analyze the presence, distribution and colocalization of the aforementioned indicators in HSG tissues.

RESULT

The mRNA and protein expression of autophagy-related proteins were significantly increased in HSG cells costimulated with LPS and MDP for 24 hours. NOD2, TLR4 and the autophagy-related proteins were also highly expressed in residual acini and dilated ducts of chronic submandibular sialadenitis tissues. In addition, PRRs and autophagy markers were obviously colocalized in chronic submandibular sialadenitis tissues and HSG cells.

CONCLUSION

TLR4 and NOD2 have unique expression sites in salivary glands, and they may synergistically activate autophagy in salivary glands under conditions of inflammation.

Schisandrin C enhances odontoblastic differentiation through autophagy and mitochondrial biogenesis in human dental pulp cells

OBJECTIVE

To investigate the role of Schisandrin C in odontoblastic differentiation, and its relations between autophagy and mitochondrial biogenesis in human dental pulp cells (HPDCs).

DESIGN

Fresh third molars were used, and cultured for HDPCs. Western blotting technique, Alizarin red S staining, alkaline phosphatase (ALP) activity, and confocal microscopy were used to detect autophagy, mitochondrial biogenesis, and odontoblastic differentiation. To understand the mechanism of Schisandrin C, the HDPCs were treated with lipopolysaccharide (LPS), autophagy and heme oxygenase-1 (HO-1) inhibitors: 3-Methyladenine (3-MA) and Zinc protoporphyrin IX (ZnPP), respectively.

RESULTS

LPS decreased the expression of autophagy molecules [autophagy protein 5 (ATG-5), beclin-1, and microtubule-associated protein 1A/1B light chain 3 (LC3-I/II)] and mitochondrial biogenesis molecules [heme oxygenase-1 (HO-1) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)], and disrupted odontoblastic differentiation. The down-regulation of autophagy and mitochondrial biogenesis with 3-MA and ZnPP inhibited odontoblastic differentiation. However, Schisandrin C restored the expression of all the above molecules, even with LPS and inhibitor treatment. This result demonstrates that autophagy and mitochondrial biogenesis plays an essential role in odontoblastic differentiation, and Schisandrin C activates these systems to promote odontoblastic differentiation of HDPCs.

CONCLUSION

Schisandrin C has potential characters to regulate odontoblastic differentiation, and may be recommended for use as a compound for pulp homeostasis.

Autophagy in the dentin-pulp complex against inflammation

The dentin-pulp complex is a highly specialized tissue for protecting the dental pulp. Odontoblasts are long-lived, hard-tissue-forming cells in the dentin-pulp complex and critically involved in inflammatory responses against invading pathogens. Autophagy is a highly conserved homeostasis mechanism of living cells under various stress conditions. Growing evidence in the literature addresses the role of autophagy in odontoblast differentiation and aging. This review summarizes the current knowledge about autophagy for the dentin-pulp complex in resisting inflammation.

Bilirubin reversibly affects cell death and odontogenic capacity in stem cells from human exfoliated deciduous teeth

OBJECTIVE

Hyperbilirubinemia in patients with biliary atresia causes deciduous tooth injuries such as green pigmentation and dentin hypoplasia. In patients with biliary atresia who received liver transplantation, tooth structure appears to be recovered radiographically. Nevertheless, little is known about cellular mechanisms underlying bilirubin-induced damage and suppression of deciduous tooth formation. In this study, we examined the effects of bilirubin in stem cells from human exfoliated deciduous teeth (SHED) in vitro.

MATERIALS AND METHODS

SHED were cultured under exposure to excess of bilirubin and then interruption of bilirubin stimulation.

RESULTS

Bilirubin induced cell death and inhibited the odontogenic capacity of SHED by suppressing AKT and extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathways and enhancing nuclear factor kappa B p65 (NF-κB p65) pathway. The interruption of bilirubin stimulation reduced cell death and recovered the inhibited odontogenic capacity of bilirubin-damaged SHED. The bilirubin interruption also normalized the impaired AKT, ERK1/2, and NF-κB p65 signaling pathways.

CONCLUSION

These findings suggest that tooth hypodontia in patients with hyperbilirubinemia might be due to bilirubin-induced cell death and dentinogenic dysfunction of odontogenic stem cells via AKT, ERK1/2, and NF-κB pathways and also suggested that bilirubin-induced impairments in odontogenic stem cells were reversible when bilirubin stimulation is interrupted.

Mitofusin 2 Promotes Apoptosis of CD4+ T Cells by Inhibiting Autophagy in Sepsis

Apoptosis of CD4⁺ T cells is a primary pathophysiological mechanism of immune dysfunction in the pathogenesis of sepsis. Mitofusin 2 (Mfn2), an integral mitochondrial outer membrane protein, has been confirmed to be associated with cellular metabolism, proliferation, and apoptosis. The function of Mfn2 in CD4⁺ T cell apoptosis in sepsis is poorly understood. Here, we discovered increased in vivo Mfn2 expression, autophagy deficiency, and elevated cell apoptosis in murine splenic CD4⁺ T cells after cecal ligation and puncture (CLP). We also observed almost identical results in splenic CD4⁺ T cells upon lipopolysaccharide (LPS) stimulation in vitro. Furthermore, overexpression of Mfn2 resulted in impaired autophagy and increased apoptosis in Jurkat cells. Pharmacological inhibition of autophagy with 3-methyladenine enhanced Mfn2 overexpression-induced cell apoptosis. In addition, overexpression of Mfn2 downregulated phorbol myristate acetate (PMA)/ionomycin-, rapamycin- and starvation-induced autophagy in Jurkat T cells. Taken together, these data indicate a critical role of Mfn2 in CD4⁺ T cell apoptosis in sepsis and the underlying mechanism of autophagy deficiency.

The Role of Reactive Oxygen Species and Autophagy in Periodontitis and Their Potential Linkage

Periodontitis is a chronic inflammatory disease that causes damage to periodontal tissues, which include the gingiva, periodontal ligament, and alveolar bone. The major cause of periodontal tissue destruction is an inappropriate host response to microorganisms and their products. Specifically, a homeostatic imbalance between reactive oxygen species (ROS) and antioxidant defense systems has been implicated in the pathogenesis of periodontitis. Elevated levels of ROS acting as intracellular signal transducers result in autophagy, which plays a dual role in periodontitis by promoting cell death or blocking apoptosis in infected cells. Autophagy can also regulate ROS generation and scavenging. Investigations are ongoing to elucidate the crosstalk mechanisms between ROS and autophagy. Here, we review the physiological and pathological roles of ROS and autophagy in periodontal tissues. The redox-sensitive pathways related to autophagy, such as mTORC1, Beclin 1, and the Atg12-Atg5 complex, are explored in depth to provide a comprehensive overview of the crosstalk between ROS and autophagy. Based on the current evidence, we suggest that a potential linkage between ROS and autophagy is involved in the pathogenesis of periodontitis.

Autophagy and its implication in human oral diseases

Macroautophagy/autophagy is a conserved lysosomal degradation process essential for cell physiology and human health. By regulating apoptosis, inflammation, pathogen clearance, immune response and other cellular processes, autophagy acts as a modulator of pathogenesis and is a potential therapeutic target in diverse diseases. With regard to oral disease, autophagy can be problematic either when it is activated or impaired, because this process is involved in diverse functions, depending on the specific disease and its level of progression. In particular, activated autophagy functions as a cytoprotective mechanism under environmental stress conditions, which regulates tumor growth and mediates resistance to anticancer treatment in established tumors. During infections and inflammation, activated autophagy selectively delivers microbial antigens to the immune systems, and is therefore connected to the elimination of intracellular pathogens. Impaired autophagy contributes to oxidative stress, genomic instability, chronic tissue damage, inflammation and tumorigenesis, and is involved in aberrant bacterial clearance and immune priming. Hence, substantial progress in the study of autophagy provides new insights into the pathogenesis of oral diseases. This review outlines the mechanisms of autophagy, and highlights the emerging roles of this process in oral cancer, periapical lesions, periodontal diseases, and oral candidiasis.

Autophagy regulates odontoblast differentiation by suppressing NF-κB activation in an inflammatory environment

Odontoblasts are derived from dental papilla mesenchymal cells and have an important role in defense against bacterial infection, whereas autophagy can recycle long-lived proteins and damaged organelles to sustain cellular homeostasis. Thus, this study explores the role of autophagy in odontoblast differentiation with lipopolysaccharide (LPS) stimulation in vitro and the colocalization of p-NF-κB and LC3 in caries teeth. The odontoblasts differentiation was enhanced through LPS stimulation, and this outcome was reflected in the increased number of mineralized nodules and alkaline phosphatase (ALP) activity. The expression levels of the autophagy markers LC3, Atg5, Beclin1 and TFE3 increased time dependently, as well along with the amount of autophagosomes and autophagy fluxes. This result suggests that autophagy was enhanced in odontoblasts cultured with mineralized-induced media containing LPS. To confirm the role of autophagy in differentiated odontoblasts with LPS stimulation, chloroquine (CQ) or rapamycin were used to either block or enhance autophagy. The number of mineralized nodules decreased when autophagy was inhibited, but this number increased with rapamycin treatment. Phosphorylated nuclear factor-κB (NF-κB) expression was negatively related to autophagy and could inhibit odontoblast differentiation. Furthermore, p-NF-κB and LC3 colocalization could be detected in cells stimulated with LPS. The nucleus translocation of p-NF-κB in odontoblasts was enhanced when autophagy was inhibited by Atg5 small interfering RNA. In addition, the colocalization of p-NF-κB and LC3 in odontoblasts and sub-odontoblastic layers was observed in caries teeth with reactionary dentin. Therefore, our findings provide a novel insight into the role of autophagy in regulating odontoblast differentiation by suppressing NF-κB activation in inflammatory environments.

Increased Apoptosis of Inflamed Odontoblasts Is Associated with CD47 Loss

Survival of odontoblasts during infection and inflammation determines prognosis of the dental pulp. CD47 is a “self”-label surface marker on viable cells. The aim of the present study is to investigate the interaction between CD47, autophagy, and apoptosis in inflamed human dental pulp and lipopolysaccharide (LPS)–treated mDPC6T cells. We identified activation of autophagy and apoptosis in the odontoblasts due to inflammation of the human dental pulp. Furthermore, downregulation of CD47 correlated with increased autophagy and apoptosis in dental pulp of the patients afflicted with either caries and/or pulpitis. We also detected colocalization of CD47 and LC3 in the inflamed odontoblasts. In addition, functional study indicated that loss of CD47 activates autophagy and increases apoptosis, indicating that CD47 plays a key role in the LPS-induced autophagy and apoptosis of odontoblasts.