Adenosine receptors enhance the ATP-induced odontoblastic differentiation of human dental pulp cells

Increased Purinergic Signaling in Human Dental Pulps With Inflammatory Pain is Sex-Dependent

An enhanced understanding of neurotransmitter systems contributing to pain transmission aids in drug development, while the identification of biological variables like age and sex helps in the development of personalized pain management and effective clinical trial design. This study identified enhanced expression of purinergic signaling components specifically in painful inflammation, with levels increased more in women as compared to men. Inflammatory dental pain is common and potentially debilitating; as inflammation of the dental pulp can occur with or without pain, it provides a powerful model to examine distinct pain pathways in humans. In control tissues, P2X3 and P2X2 receptors colocalized with PGP9.5-positive nerves. Expression of the ecto-nucleotidase NTPDase1 (CD39) increased with exposure to extracellular adenosine triphosphate (ATP), implying CD39 acted as a marker for sustained elevation of extracellular ATP. Both immunohistochemistry and immunoblots showed P2X2, P2X3, and CD39 increased in symptomatic pulpitis, suggesting receptors and the ATP agonist were elevated in patients with increased pain. The increased expression of P2X3 and CD39 was more frequently observed in women than men. In summary, this study identifies CD39 as a marker for chronic elevation of extracellular ATP in fixed human tissue. It supports a role for increased purinergic signaling in humans with inflammatory dental pain and suggests the contribution of purines shows sexual dimorphism. This highlights the potential for P2X antagonists to treat pain in humans and stresses the need to consider sex in clinical trials that target pain and purinergic pathways. PERSPECTIVE: This article demonstrates an elevation of ATP-marker CD39 and of ATP receptors P2X2 and P2X3 with inflammatory pain and suggests the rise is greater in women. This highlights the potential for P2X antagonists to treat pain and stresses the consideration of sexual dimorphism in studies of purines and pain.

Markers of dental pulp stem cells in in vivo developmental context

Teeth and their associated tissues contain several populations of mesenchymal stem cells, one of which is represented by dental pulp stem cells (DPSCs). These cells have mainly been characterised in vitro and numerous positive and negati ve markers for these cells have been suggested. To investigate the presence and localization of these molecules during development, forming dental pulp was examined using the mouse first mandibular molar as a model. The stages corresponding to postnatal (P) days 0, 7, 14, and 21 were investigated. The expression was monitored using customised PCR Arrays. Additionally, in situ localization of the key trio of markers (Cd73, Cd90, Cd105 coded by genes Nt5e, Thy1, Eng) was performed at prenatal and postnatal stages using immunohistochemistry. The expression panel of 24 genes assigned as in vitro markers of DPSCs or mesenchymal stem cells (MSCs) revealed their developmental dynamics during formation of dental pulp mesenchyme. Among the positive markers, Vcam1, Fgf2, Nes were identified as increasing and Cd44, Cd59b, Mcam, Alcam as decreasing between perinatal vs. postnatal stages towards adulthood. Within the panel of negative DPSC markers, Cd14, Itgb2, Ptprc displayed increased and Cd24a decreased levels at later stages of pulp formation. Within the key trio of markers, Nt5e did not show any significant expression difference within the investigated period. Thy1 displayed a strong decrease between P0 and P7 while Eng increased between these stages. In situ localization of Cd73, Cd90 and Cd105 showed them overlap in differentiated odontoblasts and in the sub-odontoblastic layer that is speculated to host odontoblast progenitors. The highly prevalent expression of particularly Cd73 and Cd90 opens the question of potential multiple functions of these molecules. The results from this study add to the in vitro based knowledge by showing dynamics in the expression of DPSC/MSC markers during dental pulp formation in an in vivo context and thus with respect to the natural environment important for commitment of stem cells.

Extracellular ATP-induced calcium oscillations regulating the differentiation of osteoblasts through aerobic oxidation metabolism pathways

INTRODUCTION

The increase of ATP concentration in the extracellular space represents one of the effective signals that stimulate the physiological activities of cells when the bone is exposed to external mechanical stimulation such as stretching and shear stress force throughout life. However, the effects of ATP on osteoblast differentiation and related mechanisms are not well understood.

MATERIALS AND METHODS

In this study, the roles of extracellular ATP on osteoblast differentiation, intracellular calcium ([Ca2+]i) levels, metabolomics, and the expression of proteins related to energy metabolism were investigated.

RESULTS

Our results showed that 100 μM extracellular ATP initiated intracellular calcium ([Ca2+]i) oscillations via the calcium-sensing receptor (P2R) and promoted the differentiation of MC3T3-E1 cells. Metabolomics analysis showed that the differentiation of MC3T3-E1 cells depended on aerobic oxidation, but little glycolysis. Moreover, the differentiation of MC3T3-E1 cells and aerobic oxidation were suppressed with the inhibition of AMP-activated protein kinase (AMPK).

CONCLUSION

These results indicate that calcium oscillations triggered by extracellular ATP can activate aerobic oxidation through AMPK-related signaling pathways and thus promote osteoblast differentiation.

Functional Expression of IP, 5-HT4, D1, A2A, and VIP Receptors in Human Odontoblast Cell Line

Odontoblasts are involved in sensory generation as sensory receptor cells and in dentin formation. We previously reported that an increase in intracellular cAMP levels by cannabinoid 1 receptor activation induces Ca²⁺ influx via transient receptor potential vanilloid subfamily member 1 channels in odontoblasts, indicating that intracellular cAMP/Ca²⁺ signal coupling is involved in dentinal pain generation and reactionary dentin formation. Here, intracellular cAMP dynamics in cultured human odontoblasts were investigated to understand the detailed expression patterns of the intracellular cAMP signaling pathway activated by the G_s protein-coupled receptor and to clarify its role in cellular functions. The presence of plasma membrane Gα_s as well as prostaglandin I₂ (IP), 5-hydroxytryptamine 5-HT₄ (5-HT₄), dopamine D₁ (D₁), adenosine A_2A (A_2A), and vasoactive intestinal polypeptide (VIP) receptor immunoreactivity was observed in human odontoblasts. In the presence of extracellular Ca²⁺, the application of agonists for the IP (beraprost), 5-HT₄ (BIMU8), D₁ (SKF83959), A_2A (PSB0777), and VIP (VIP) receptors increased intracellular cAMP levels. This increase in cAMP levels was inhibited by the application of the adenylyl cyclase (AC) inhibitor SQ22536 and each receptor antagonist, dose-dependently. These results suggested that odontoblasts express G_s protein-coupled IP, 5-HT₄, D₁, A_2A, and VIP receptors. In addition, activation of these receptors increased intracellular cAMP levels by activating AC in odontoblasts.

Effect of Cordyceps spp. and Cordycepin on Functions of Bones and Teeth and Related Processes: A Review

Cordyceps spp. (belonging to the Ascomycota group) are entomopathogenic mushrooms that have traditionally been used in ethnomedicine in Asian countries such as China, Japan, Korea, and India. They are unique parasites of larvae of selected species of moths. Cordyceps militaris is one of the best sources of cordycepin. Worldwide, osteoporosis is one of the most common bone diseases, whose pharmacotherapy includes various medical interventions; however, the research and development of new molecules and new drugs is required. The impact of adenosine receptors (ARs) on the purinergic signaling pathway may regulate proliferation, differentiate dental pulp stem cells and bone marrow, and modulate osteogenesis and bone repair. The aim of the review was to collect and analyze the available data on the effects of Cordyceps spp. or cordycepin on bone function and related processes. To the best of our knowledge, this is the first systematic review in this perspective, not necessarily using mushroom raw material or even the isolated parent compound cordycepin, but new molecules that are analogs of nucleosides, such as those from C. militaris. This review found that Cordyceps spp. or isolated cordycepin interacts via the AR, 5' adenosine monophosphate-activated protein kinase (AMPK), and adenosine-5'-triphosphate (ATP) signaling pathway and evaluated their impact on bones, teeth, and dental pulp. Cordyceps spp. was found to have the potential to develop regenerative medicines, thus providing an opportunity to expand the treatment or intervention methods in the recovery after traumatic injuries, convalescence, and terminal-stage or devastating diseases.

Purinergic Signaling in Oral Tissues

The role of the purinergic signal has been extensively investigated in many tissues and related organs, including the central and peripheral nervous systems as well as the gastrointestinal, cardiovascular, respiratory, renal, and immune systems. Less attention has been paid to the influence of purines in the oral cavity, which is the first part of the digestive apparatus and also acts as the body’s first antimicrobial barrier. In this review, evidence is provided of the presence and possible physiological role of the purinergic system in the different structures forming the oral cavity including teeth, tongue, hard palate, and soft palate with their annexes such as taste buds, salivary glands, and nervous fibers innervating the oral structures. We also report findings on the involvement of the purinergic signal in pathological conditions affecting the oral apparatus such as Sjögren’s syndrome or following irradiation for the treatment of head and neck cancer, and the use of experimental drugs interfering with the purine system to improve bone healing after damage. Further investigations are required to translate the results obtained so far into the clinical setting in order to pave the way for a wider application of purine-based treatments in oral diseases.

Human dental pulp stem cells and hormesis

This paper represents the first assessment of hormetic dose responses by human dental pulp stem cells (hDPSCs) with particular emphasis on cell renewal (proliferation) and differentiation. Hormetic dose responses were commonly reported in this model, encompassing a broad range of chemicals, including principally pharmaceuticals (e.g., metformin and artemisinin), dietary supplements/extracts from medicinal plants (e.g., berberine, N-acetyl-L-cysteine, and ginsenoside Rg1) and endogenous agents (e.g., ATP, TNF-α). The paper assesses mechanistic foundations of the hDPSCs hormetic dose responses for both cell proliferation and cell differentiation, study design considerations, and therapeutic implications.

Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

Time-Dependent Response of Human Deciduous Tooth-Derived Dental Pulp Cells Treated with TheraCal LC: Functional Analysis of Gene Interactions Compared to MTA

Pulp capping material should facilitate hard tissue regeneration on the injured pulp tissue. TheraCal LC (TC) was recently developed. Although TC has shown reliable clinical outcomes after direct pulp capping, there are still remaining concerns regarding its detrimental effect on pulp cells. Therefore, this study aimed to identify the gene expression of human deciduous tooth-derived dental pulp cells exposed to TC compared to mineral trioxide aggregate (MTA). The cells were cultured and exposed to TC and MTA for 24 and 72 h. Next, total RNA was isolated. QuantSeq 3′ mRNA-sequencing was used to examine differentially expressed genes (DEGs) in exposed to TC and MTA. Functional analysis of DEGs was performed using bioinformatics analysis. In gene ontology (GO) functional enrichment analysis, cells in TC for 24 h presented significantly enriched immune response (p < 0.001) and inflammatory response (p < 0.01) compared to MTA. TC showed enriched positive regulation of cell migration at 72 h (p < 0.001). In Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, neuroactive ligand–receptor interaction (p = 1.19 × 10⁻⁷) and calcium signaling pathway (p = 2.96 × 10⁻⁵) were confirmed in the shared DEGs in TC. In conclusion, DEGs in TC may be involved in pathways associated with osteoclastogenesis and osteoclastic differentiation.

Interaction of Nel-like molecule 1 with apoptosis related protein 3 with its influence on human dental pulp cells proliferation and differentiation into odontoblasts

Nel-like molecule 1 (Nell-1) is an essential positive regulator of tooth development and odontoblast differentiation. However, its precise mechanism remains undetermined. This study aims to explore the possible receptor or binding protein of Nell-1. Results showed that Nell-1 and Apoptosis related protein 3(APR3) expression levels were high in odontoblasts and inversely correlated. Endogenous Nell-1 co-immunoprecipitated with APR3, and this co-IP was reciprocal. Double immunofluorescence staining revealed that Nell-1 and APR3 colocalized on the nuclear envelope of human dental pulp cells. Nell-1 inhibited the proliferation of these cells co-infected with APR3 through Cyclin D1 downregulation. The interaction of Nell-1 with APR3 stimulated alkaline phosphatase (ALP) activity and promoted the expression and mineralization of DSPP, ALP, OPN, and BSP. The shRNA of APR3 decreased cell differentiation and mineralization. Nell-1 could reciprocally interact with APR3 and stimulate the differentiation and mineralization of human dental pulp cells. Future studies should explore the potential functional connection and the molar mechanism of such interaction.