Development of a Direct Pulp-capping Model for the Evaluation of Pulpal Wound Healing and Reparative Dentin Formation in Mice

A novel experimental model to investigate fungal involvement shows expression of Dectin-1 in periapical lesion pathogenesis

BACKGROUND

Candida albicans is linked to persistent endodontic lesions. However, the recognition receptor that identifies it is not explored previously.

OBJECTIVES

The aim of this study was to (1) establish a zymosan-induced model of apical periodontitis in mouse, (2) observe the expression of Dectin-1 and its possible relationship with toll-like receptor (TLR) 2 and (3) observe relationship between Osteopontin (OPN) and inflammatory cytokines.

METHODS

A total of 138 Naval Medical Research Institute (NMRI) mice were randomly divided into; Experimental Group n = 69 and Zymosan Group n = 69. Periapical periodontitis was developed in right maxillary molar. The animals were sacrificed at 7, 21 and 42 days. Bone blocks containing the mesial root (n = 15 for qRT-PCR, n = 45 for enzyme-linked immune sorbent assay (ELISA)) were collected for mRNA expression and ELISA. While whole maxilla (n = 3 from each time interval) were used for histology and immunohistochemical analysis. One way analysis of variance (ANOVA) and Tuckey's posthoc was used for statistical analysis at p ≤ .05.

RESULTS

TLR-2, Dectin-1 and TLR4-positive cells was detected at all time intervals in both groups. A strong positive correlation was observed between TLR-2 and Dectin-1 in both lesions (regular r = .680, p = .015, zymosan (r = .861, p < .001)). A significant correlation was found between OPN and tumour necrosis factor-alpha (TNF-α) in zymosan lesion (r = .827, p = .001).

CONCLUSIONS

Immune cells of inflamed periapical tissue expressed Dectin-1 receptor in response to the microbial challenge from infected root canals and showed positive correlation with TLR-2 and OPN suggesting a possible receptor collaboration mediated by OPN. The expression of OPN and TNF-α showed positive correlation in response to fungal antigen, indicating a possible relationship.

The effect of BMP9 on inflammation in the early stage of pulpitis

BACKGROUND

Bone morphogenetic protein 9 (BMP9) tends to be associated with various inflammatory responses of diseases, but its relationship with pulpitis remains unknown.

OBJECTIVE

This study aimed to evaluate the effects and mechanisms of BMP9 in pulpitis.

METHODOLOGY

A rat model of pulpitis was used to evaluate the expression of BMP9, which was also analysed in Porphyromonas gingivalis lipopolysaccharide (Pg-LPS)-stimulated human dental pulp cells (hDPCs). The effects and mechanism of BMP9 on the regulation of inflammatory factors and matrix metalloproteinase-2 (MMP2) were evaluated using real-time quantitative PCR, western blotting, and immunocytofluorescence. Moreover, the migration ability of THP-1 monocyte-macrophages, treated with inflammatory supernate inhibited by BMP9, was previously tested by a transwell migration assay. Finally, a direct rat pulp capping model was used to evaluate in vivo the influence of the overexpression of BMP9 in pulpitis.

RESULTS

The expression of BMP9 decreased after 24 h and increased after 3 and 7 d in rat pulpitis and inflammatory hDPCs. The overexpression of BMP9 inhibited the gene expression of inflammatory factors (IL-6, IL-8, and CCL2) and the secretion of IL-6 and MMP2 in Pg-LPS-stimulated hDPCs. The level of phosphorylated Smad1/5 was upregulated and the levels of phosphorylated ERK and JNK were downregulated. The inflammatory supernate of hDPCs inhibited by BMP9 reduced the migration of THP-1 cells. In rat pulp capping models, overexpressed BMP9 could partially restrain the development of dental pulp inflammation.

CONCLUSION

This is the first study to confirm that BMP9 is involved in the occurrence and development of pulpitis and can partially inhibit its severity in the early stage. These findings provided a theoretical reference for future studies on the mechanism of pulpitis and application of bioactive molecules in vital pulp therapy.

Stage-specific requirement for METTL3-dependent m6A modification during dental pulp stem cell differentiation

BACKGROUND

N⁶-methyladenosine (m⁶A) is the most prevalent epigenetic modification in eukaryotic messenger RNAs and plays a critical role in cell fate transition. However, it remains to be elucidated how m⁶A marks functionally impact the transcriptional cascades that orchestrate stem cell differentiation. The present study focuses on the biological function and mechanism of m⁶A methylation in dental pulp stem cell (DPSC) differentiation.

METHODS

m⁶A RNA immunoprecipitation sequencing was utilized to assess the m⁶A-mRNA landscape during DPSC differentiation. Ectopic transplantation of DPSCs in immunodeficient mice was conducted to verify the in vitro findings. RNA sequencing and m⁶A RNA immunoprecipitation sequencing were combined to identify the candidate targets. RNA immunoprecipitation and RNA/protein stability of Noggin (NOG) were evaluated. The alteration in poly(A) tail was measured by 3'-RACE and poly(A) tail length assays.

RESULTS

We characterized a dynamic m⁶A-mRNA landscape during DPSC mineralization with increasing enrichment in the 3' untranslated region (UTR). Methyltransferase-like 3 (METTL3) was identified as the key m⁶A player, and METTL3 knockdown disrupted functional DPSC differentiation. Moreover, METTL3 overexpression enhanced DPSC mineralization. Increasing m⁶A deposition in the 3' UTR restricted NOG expression, which is required for DPSC mineralization. This stage-specific m⁶A methylation and destabilization of NOG was suppressed by METTL3 knockdown only in differentiated DPSCs. Furthermore, METTL3 promotes the degradation of m⁶A-tagged NOG by shortening the poly(A) tail length in the differentiated stage.

CONCLUSIONS

Our results address an essential role of dynamic m⁶A signaling in the temporal control of DPSC differentiation and provide new insight into epitranscriptomic mechanisms in stem cell-based therapy.

Indigenous microbiota protects development of medication-related osteonecrosis induced by periapical disease in mice

Bacterial infection is a common finding in patients, who develop medication-related osteonecrosis of the jaw (MRONJ) by the long-term and/or high-dose use of anti-resorptive agents such as bisphosphonate (BPs). However, pathological role of bacteria in MRONJ development at the early stage remains controversial. Here, we demonstrated that commensal microbiota protects against MRONJ development in the pulp-exposed periapical periodontitis mouse model. C57/BL6 female mice were treated with intragastric broad-spectrum antibiotics for 1 week. Zoledronic acid (ZOL) through intravenous injection and antibiotics in drinking water were administered for throughout the experiment. Pulp was exposed on the left maxillary first molar, then the mice were left for 5 weeks after which bilateral maxillary first molar was extracted and mice were left for additional 3 weeks to heal. All mice were harvested, and cecum, maxilla, and femurs were collected. ONJ development was assessed using μCT and histologic analyses. When antibiotic was treated in mice, these mice had no weight changes, but developed significantly enlarged ceca compared to the control group (CTL mice). Periapical bone resorption prior to the tooth extraction was similarly prevented when treated with antibiotics, which was confirmed by decreased osteoclasts and inflammation. ZOL treatment with pulp exposure significantly increased bone necrosis as determined by empty lacunae and necrotic bone amount. Furthermore, antibiotics treatment could further exacerbate bone necrosis, with increased osteoclast number. Our findings suggest that the commensal microbiome may play protective role, rather than pathological role, in the early stages of MRONJ development.

Effects of rice fermented extracts, "Sake Lees", on the functional activity of odontoblast-like cells (KN-3 cells)

This study was designed to investigate the effects of Sake Lees extracts (SLE, Sake Kasu) on the functional activity of odontoblastic cells and tooth pulp of the rats. For in vitro studies, a rat clonal odontoblast-like cell line, KN-3 cells were cultured. SLE significantly decreased KN-3 cell proliferation, but showed no significant cytotoxicity. SLE effects on several protein productions of KN-3 cells were compared with PBS. SLE and PBS increased alkaline phosphatase (ALP), dentin sialoprotein (DSP), and osterix in a day-course dependent manner, while SLE increased the induction of ALP on day 9-21 and DSP on day 15-21. SLE also increased Runx2 expression on day 3 and 9 compared to PBS. Alizarin Red stainings revealed that SLE showed a subtle increase in mineralization of KN-3 cells on day 15 and 21. A histological investigation was conducted to assess if SLE induced reparative dentin formation after direct capping at the exposed tooth pulp in rats, suggesting that SLE could increase the reparative dentin formation more than PBS. These findings suggest that Sake Lees could have functional roles in the alterations of odontoblastic activity, which might influence the physiology of the tooth pulp.

Nanoparticles of Bioactive Glass Enhance Biodentine Bioactivity on Dental Pulp Stem Cells

This study aimed to investigate the cytotoxicity and bioactivity of a novel nanocomposite containing nanoparticles of bioactive glass (nBGs) on human dental pulp stem cells (hDPSCs). nBGs were synthesized by the sol–gel method. Biodentine (BD) nanocomposites (nBG/BD) were prepared with 2 and 5% wt of nBG content; unmodified BD and glass ionomer cement were used as references. Cell viability and attachment were evaluated after 3, 7 and 14 days. Odontogenic differentiation was assessed with alkaline phosphatase (ALP) activity after 7 and 14 days of exposure. Cells successfully adhered and proliferated on nBG/BD nanocomposites, cell viability of nanocomposites was comparable with unmodified BD and higher than GIC. nBG/BD nanocomposites were, particularly, more active to promote odontogenic differentiation, expressed as higher ALP activity of hDPSCs after 7 days of exposure, than neat BD or GIC. This novel nanocomposite biomaterial, nBG/BD, allowed hDPSC attachment and proliferation and increased the expression of ALP, upregulated in mineral-producing cells. These findings open opportunities to use nBG/BD in vital pulp therapies.

Transcriptomic Classification of Neurons Innervating Teeth

Toothache is a common painful consequence of damage to the teeth, particularly when coupled to infection. Clinical restoration of tooth integrity, sometimes involving physical and chemical sterilization of the tooth with nerve fiber ablation (i.e., endodontic therapy), generally alleviates pain and allows long-lasting dental function. These observations raise questions regarding the biological role of tooth-innervating fibers. Here, we determined the transcriptomic diversity of the sensory neurons that can be retrogradely labeled from mouse molar teeth. Our results demonstrate that individual molars are each targeted by a dedicated population of about 50 specialized trigeminal neurons. Transcriptomic profiling identifies the majority of these as expressing markers of fast-conducting neurons, with about two-thirds containing nociceptive markers. Our data provide a new view of dental innervation, extending previous reports that used candidate gene approaches. Importantly, almost all retrogradely labeled neurons, including nociceptors, express the recently characterized mechanosensor Piezo2, an ion channel that endows cells with sensitivity to gentle touch. Intriguingly, about a quarter of the labeled neurons do not appear to be nociceptors, perhaps insinuating a role for them in discriminative touch. We hypothesize that dental neurons are capable of providing mechanosensitive information to drive rapid behavioral responses and protect teeth from damage. Damage to the teeth and exposure of the large population of molar nociceptors may trigger prolonged or abnormal activation driving toothache. Future studies examining the responses of these transcriptomically defined classes of neurons will help define their significance in oral sensation.