Macrophage populations show an M1-to-M2 transition in an experimental model of coronal pulp tissue engineering with mesenchymal stem cells

Analysis of macrophage polarization and regulation characteristics in ovarian tissues of polycystic ovary syndrome

Background

Polycystic ovary syndrome (PCOS) can lead to infertility and increase the risk of endometrial cancer. Analyzing the macrophage polarization characteristics in ovarian tissues of PCOS is crucial for clinical treatment.

Methods

We obtained 13 PCOS and nine control ovarian samples from the CEO database and analyzed differentially expressed genes (DEGs). Macrophage polarization-related genes (MPRGs) were sourced from the GeneCards and MSigDB databases. Intersection of DEGs with MPRGs identified DEGs associated with macrophage polarization (MPRDEGs). Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Protein-protein interaction (PPI) Network analysis were conducted on MPRDEGs. Moreover, the top 10 genes from three algorithms were identified as the hub genes of MPRGs. In addition, miRNAs, transcription factors (TFs), and drugs were retrieved from relevant databases for regulatory network analysis of mRNA-miRNA, mRNA-TF, and mRNA-Drug interactions. Immune cell composition analysis between the PCOS and control groups was performed using the CIBERSORT algorithm to calculate correlations across 22 immune cell types.

Results

A total of 13 PCOS samples and nine control ovarian samples were obtained in this study. We identified 714 DEGs between the two groups, with 394 up-regulated and 320 down-regulated. Additionally, we identified 774 MPRGs, from which we derived 30 MPRDEGs by intersecting with DEGs, among which 21 exhibited interaction relationships. GO and KEGG analyses revealed the enrichment of MPRDEGs in five biological processes, five cell components, five molecular functions, and three biological pathways. Immune infiltration analysis indicated a strong positive correlation between activated nature killer (NK) cells and memory B cells, while neutrophils and monocytes showed the strongest negative correlation. Further investigation of MPRDEGs identified nine hub genes associated with 41 TFs, 82 miRNAs, and 44 drugs or molecular compounds. Additionally, qRT-PCR results demonstrated overexpression of the CD163, TREM1, and TREM2 genes in ovarian tissues from the PCOS group.

Conclusion

This study elucidated the polarization status and regulatory characteristics of macrophages in ovarian tissues of the PCOS subjects, confirming significant overexpression of CD163, TREM1, and TREM2. These findings contribute to a deeper understanding of the pathogenesis of PCOS.

Immune System of Dental Pulp in Inflamed and Normal Tissue

Teeth are vulnerable to structural compromise, primarily attributed to carious lesions, in which microorganisms originating from the oral cavity deteriorate the mineralized structures of enamel and dentin, subsequently infiltrating the underlying soft connective tissue, known as the dental pulp. Nonetheless, dental pulp possesses the necessary capabilities to detect and defend against bacteria and their by-products, using a variety of intricate defense mechanisms. The pulp houses specialized cells known as odontoblasts, which encounter harmful substances produced by oral bacteria. These cells identify pathogens at an early stage and commence the immune system response. As bacteria approach the pulp, various cell types within the pulp, such as different immune cells, stem cells, fibroblasts, as well as neuronal and vascular networks, contribute a range of defense mechanisms. Therefore, the immune system is present in the healthy pulp to restrain the initial spread of pathogens, and then in the inflamed pulp, it prepares the conditions for necrosis or regeneration, so inflammatory response mechanisms play a critical role in maintaining tissue homeostasis. This review aims to consolidate the existing literature on the immune system in dental pulp, encompassing current knowledge on this topic that explains the diverse mechanisms of recognition and defense against pathogens exhibited by dental pulp cells, elucidates the mechanisms of innate and adaptive immunity in inflamed pulp, and highlights the difference between inflamed and normal pulp tissue.

Research and development of microenvironment's influence on stem cells from the apical papilla - construction of novel research microdevices: tooth-on-a-chip

Stem cells are crucial in tissue engineering, and their microenvironment greatly influences their behavior. Among the various dental stem cell types, stem cells from the apical papilla (SCAPs) have shown great potential for regenerating the pulp-dentin complex. Microenvironmental cues that affect SCAPs include physical and biochemical factors. To research optimal pulp-dentin complex regeneration, researchers have developed several models of controlled biomimetic microenvironments, ranging from in vivo animal models to in vitro models, including two-dimensional cultures and three-dimensional devices. Among these models, the most powerful tool is a microfluidic microdevice, a tooth-on-a-chip with high spatial resolution of microstructures and precise microenvironment control. In this review, we start with the SCAP microenvironment in the regeneration of pulp-dentin complexes and discuss research models and studies related to the biological process.

An injectable dental pulp-derived decellularized matrix hydrogel promotes dentin repair through modulation of macrophage response

Maintaining the viability of damaged pulp is critical in clinical dentistry. Pulp capping, by placing dental material over the exposed pulp, is a main approach to promote pulp-dentin healing and mineralized tissue formation. The dental materials are desired to impact on intricate physiological mechanisms in the healing process, including early regulation of inflammation, immunity, and cellular events. In this study, we developed an injectable dental pulp-derived decellularized matrix (DPM) hydrogel to modulate macrophage responses and promote dentin repair. The DPM derived from porcine dental pulp has high collagen retention and low DNA content. The DPM was solubilized by pepsin digestion (named p-DPM) and subsequently injected through a 25G needle to form hydrogel facilely at 37 °C. In vitro results demonstrated that the p-DPM induced the M2-polarization of macrophages and the migration, proliferation, and dentin differentiation of human dental pulp stem cells from deciduous teeth (SHEDs). In a mouse subcutaneous injection test, the p-DPM hydrogel was found to facilitate cell recruitment and M2 polarization during the early phase of implantation. Additionally, the acute pulp restoration in rat models proved that injectable p-DPM hydrogel as a pulp-capping agent had excellent efficacy in dentin regeneration. This study demonstrates that the DPM promotes dentin repair by modulating macrophage responses, and has a potential for pulp-capping applications in dental practice.

Analysis of the effect of CCR7 on the microenvironment of mouse oral squamous cell carcinoma by single-cell RNA sequencing technology

BACKGROUND

Studies have shown that CCR7, an important inflammatory factor, can promote the proliferation and metastasis of oral squamous cell carcinoma (OSCC), but its role in the tumor microenvironment (TME) remains unclear. This paper explores the role of CCR7 in the TME of OSCC.

METHODS

In this work, we constructed CCR7 gene knockout mice and OSCC mouse models. Single-cell RNA sequencing (scRNA-seq) and bioinformatics were used to analyze the differences in the OSCC microenvironment between three CCR7 gene knockout mice (KO) and three wild-type mice (WT). Immunohistochemistry, immunofluorescence staining, and flow cytometry were used to analyze the expression of key genes in significantly different cell types between the KO and WT groups. An in vitro experiment was used to verify the effect of CCR7 on M2 macrophage polarization.

RESULTS

In the mouse OSCC models, the tumor growth rate in the KO group was significantly lower than that in the WT group. Eight main cell types (including tumor cells, fibroblasts, macrophages, granulocytes, T cells, endothelial cells, monocytes, and B cells) were identified by Seurat analysis. The scRNA-seq results showed that the proportion of tumor cells was lower, but the proportion of inflammatory cells was significantly higher in the KO group than in the WT group. CellPhoneDB analysis results indicated a strong interaction relationship between tumor cells and macrophages, T cells, fibroblasts, and endothelial cells. Functional enrichment results indicated that the expression level of the Dusp1 gene in the KO group was generally higher than that in the WT group in various cell types. Macrophage subclustering results indicated that the proportion of M2 macrophages in the KO group was lower than that in the WT group. In vitro experimental results showed that CCR7 can promote M2 macrophage polarization, thus promoting the proliferation, invasion and migration of OSCC cells.

CONCLUSIONS

CCR7 gene knockout can significantly inhibit the growth of mouse oral squamous cell carcinoma by promoting the polarization of M2 macrophages.

Multifunctional Exosomes Derived from M2 Macrophages with Enhanced Odontogenesis, Neurogenesis and Angiogenesis for Regenerative Endodontic Therapy: An In Vitro and In Vivo Investigation

INTRODUCTION

Exosomes derived from M2 macrophages (M2-Exos) exhibit tremendous potential for inducing tissue repair and regeneration. Herein, this study was designed to elucidate the biological roles of M2-Exos in regenerative endodontic therapy (RET) compared with exosomes from M1 macrophages (M1-Exos).

METHODS

The internalization of M1-Exos and M2-Exos by dental pulp stem cells (DPSCs) and human umbilical vein endothelial cells (HUVECs) was detected by uptake assay. The effects of M1-Exos and M2-Exos on DPSC and HUVEC behaviors, including migration, proliferation, odonto/osteogenesis, neurogenesis, and angiogenesis were determined in vitro. Then, Matrigel plugs incorporating M2-Exos were transplanted subcutaneously into nude mice. Immunostaining for vascular endothelial growth factor (VEGF) and CD31 was performed to validate capillary-like networks.

RESULTS

M1-Exos and M2-Exos were effectively absorbed by DPSCs and HUVECs. Compared with M1-Exos, M2-Exos considerably facilitated the proliferation and migration of DPSCs and HUVECs. Furthermore, M2-Exos robustly promoted ALP activity, mineral nodule deposition, and the odonto/osteogenic marker expression of DPSCs, indicating the powerful odonto/osteogenic potential of M2-Exos. In sharp contrast with M1-Exos, which inhibited the neurogenic capacity of DPSCs, M2-Exos contributed to a significantly augmented expression of neurogenic genes and the stronger immunostaining of Nestin. Consistent with remarkably enhanced angiogenic markers and tubular structure formation in DPSCs and HUVECs in vitro, the employment of M2-Exos gave rise to more abundant vascular networks, dramatically higher VEGF expression, and widely spread CD31+ tubular lumens in vivo, supporting the enormous pro-angiogenic capability of M2-Exos.

CONCLUSIONS

The multifaceted roles of M2-Exos in ameliorating DPSC and HUVEC functions potentially contribute to complete functional pulp-dentin complex regeneration.

Exosomes derived from odontogenic stem cells: Its role in the dentin-pulp complex

Odontogenic stem cells originate from cranial neural crest cells and offer unique advantages in the regeneration of dentin-pulp complex. There is increasing evidence that stem cells exert their biological functions mainly through exosome-based paracrine effects. Exosomes contain DNA, RNA, proteins, metabolites, etc., which can play a role in intercellular communication and have similar therapeutic potential to stem cells. In addition, compared with stem cells, exosomes also have the advantages of good biocompatibility, high drug carrying capacity, easy to obtain, and few side effects. Odontogenic stem cell-derived exosomes mainly affect the regeneration of the dentin-pulp complex by regulating processes such as dentintogenesis, angiogenesis, neuroprotection and immunomodulation. This review aimed to describe "cell-free therapies" based on odontogenic stem cell-derived exosomes, which aim to regenerate the dentin-pulp complex.

Multifunctional and biodegradable methacrylated gelatin/Aloe vera nanofibers for endodontic disinfection and immunomodulation

Currently employed approaches and materials used for vital pulp therapies (VPTs) and regenerative endodontic procedures (REPs) lack the efficacy to predictably achieve successful outcomes due to their inability to achieve adequate disinfection and/or lack of desired immune modulatory effects. Natural polymers and medicinal herbs are biocompatible, biodegradable, and present several therapeutic benefits and immune-modulatory properties; thus, standing out as a clinically viable approach capable of establishing a conducive environment devoid of bacteria and inflammation to support continued root development, dentinal bridge formation, and dental pulp tissue regeneration. However, the low stability and poor mechanical properties of the natural compounds have limited their application as potential biomaterials for endodontic procedures. In this study, Aloe vera (AV), as a natural antimicrobial and anti-inflammatory agent, was incorporated into photocrosslinkable Gelatin methacrylate (GelMA) nanofibers with the purpose of developing a highly biocompatible biomaterial capable of eradicating endodontic infection and modulating inflammation. Stable GelMA/AV nanofibers with optimal properties were obtained at the ratio of (70:30) by electrospinning. In addition to the pronounced antibacterial effect against Enterococcus faecalis, the GelMA/AV (70:30) nanofibers also exhibited a sustained antibacterial activity over 14 days and significant biofilm reduction with minimal cytotoxicity, as well as anti-inflammatory properties and immunomodulatory effects favoring healing. Our results indicate that the novel GelMA/AV (70:30) nanofibers hold great potential as a biomaterial strategy for endodontic infection eradication and enhanced healing.

DDIT3 aggravates pulpitis by modulating M1 polarization through EGR1 in macrophages

DNA damage-inducible transcript 3 (DDIT3), a stress response gene, engages in the physiological and pathological processes of organisms, whereas its impact on pulpitis has not been defined yet. It has been demonstrated that macrophage polarization has a significant impact on inflammation. This research intends to investigate the effect of DDIT3 on the inflammation of pulpitis and macrophage polarization. C57BL/6J mice were used to model experimental pulpitis at 6, 12, 24, and 72 h after pulp exposure, with untreated mice as the control. The progression of pulpitis was visible histologically, and DDIT3 showed a trend of initially upward and downward later. Compared with wild-type mice, inflammatory cytokines and M1 macrophages were reduced, while M2 macrophages were increased in DDIT3 knockout mice. In RAW264.7 cells and bone borrow-derived macrophages, DDIT3 was found to enhance M1 polarization while impair M2 polarization. Targeted knockdown of early growth response 1 (EGR1) could rescue the blocking effect of DDIT3 deletion on M1 polarization. In conclusion, our results indicated that DDIT3 could exacerbate inflammation of pulpitis through the regulation of macrophage polarization, and DDIT3 could promote M1 polarization by inhibiting EGR1. It provides a new target for pulpitis treatment and tissue regeneration in the future.

Exploration of 2D and 2.5D Conformational Designs Applied on Epoxide/Collagen-Based Integrative Biointerfaces with Device/Tissue Heterogeneous Affinity

Collagen and multifunctional epoxides, which are respectively the common constituents of natural and polymer interfaces, were combined to fabricate integrative biointerfaces with device/tissue heterogeneous affinity. Further, the traditional 2D and advanced 2.5D conformational designs were achieved on collagen-based biointerfaces. The 2D conformational biointerfaces were formed by the self-entanglement of collagen molecules based on extensive hydrogen bonds among molecules, and the lamellar structures of 2D conformational biointerfaces could act as barriers to protect both biointerfaces and substrates from enzymes and corrosion. The unique stacking structures of 2.5D conformational biointerfaces were formed by cross-linking microaggregates that were established and connected by epoxy cross-linking bonds and provided the extra 0.5D degree of freedom on structure design and functional specialization through artificially manipulating the constituents and density of microaggregates. Besides, the intersecting channels among microaggregates gave 2.5D biointerfaces diffusion behaviors, which further brought good wettability and biodegradability. The integrative biointerfaces behaved well on cell viability and enhanced the cell adhesion strength in vitro, which could be attributed to the collaborations of collagen and epoxy groups. The subcutaneous implant model in rats was utilized to investigate soft tissue response, and the results demonstrated that the tissues around implantation areas healed well and without calcification or infection. The coating of integrative biointerfaces alleviated the fibrosis around implantation areas, and the inflammatory responses and foreign body reactions were improved.

Development of Rat Caries-Induced Pulpitis Model for Vital Pulp Therapy

Rodent animal models for vital pulp therapy are commonly used in dental research because their tooth anatomy and cellular processes are similar to the anatomy and processes in humans. However, most studies have been conducted using uninfected sound teeth, which makes it difficult to adequately assess the inflammatory shift after vital pulp therapy. In the present study, we aimed to establish a caries-induced pulpitis model based on the conventional rat caries model and then evaluate inflammatory changes during the wound-healing process after pulp capping in a model of reversible pulpitis induced by carious infection. To establish the caries-induced pulpitis model, the pulpal inflammatory status was investigated at different stages of caries progression by immunostaining targeted to specific inflammatory biomarkers. Immunohistochemical staining revealed that both Toll-like receptor 2 and proliferating cell nuclear antigen were expressed in moderate and severe caries-stimulated pulp, indicating that an immune reaction occurred at both stages of caries progression. M2 macrophages were predominant in moderate caries-stimulated pulp, whereas M1 macrophages were predominant in the severe caries-stimulated pulp. Pulp capping in teeth with moderate caries (i.e., teeth with reversible pulpitis) led to complete tertiary dentin formation within 28 d after treatment. Impaired wound healing was observed in teeth with severe caries (i.e., teeth with irreversible pulpitis). During the wound-healing process in reversible pulpitis after pulp capping, M2 macrophages were predominant at all time points; their proliferative capacity was upregulated in the early stage of wound healing compared with healthy pulp. In conclusion, we successfully established a caries-induced pulpitis model for studies of vital pulp therapy. M2 macrophages have an important role in the early stages of the wound-healing process in reversible pulpitis.

Peptidyl arginine deiminase expression and macrophage polarization following stimulation with citrullinated and malondialdehyde-acetaldehyde modified fibrinogen

OBJECTIVE

Post-translational modifications of extracellular matrix proteins such as fibrinogen may lead to tolerance loss and have been implicated in rheumatoid arthritis (RA) pathogenesis. The purpose of this study was to determine whether fibrinogen (FIB) modified with citrulline (CIT), malondialdehyde-acetaldehyde (MAA) or both leads to altered macrophage polarization, peptidyl arginine deiminase (PAD) expression, or production of citrullinated proteins.

METHODS

PMA-treated U-937 cells (M0 cells) were stimulated with MAA, CIT or MAA-CIT modified FIB. Macrophage (M1/M2) phenotypes were evaluated by flow cytometry, RT-PCR, and ELISA. PAD enzyme expression and protein citrullination was evaluated using RT-PCR and Western Blot.

RESULTS

Flow cytometry revealed that M0 macrophages stimulated with FIB-MAA-CIT resulted in mixed M1/M2 phenotypes as demonstrated by cell surface expression and mRNA levels of CD14, CD192, CD163, and CD206 (p < 0.001 vs. others), and the release of IL-18, IP-10, CCL22, and IL-13 (p < 0.001 vs. others). While FIB-MAA treated M0 cells demonstrated a mixed M1/M2 phenotype, cytokine and cell surface markers differed from FIB-MAA-CIT. Finally, M0 cells treated with FIB-CIT demonstrated markers and cytokines consistent with only the M1-like phenotype. Exposure of M0 cells to FIB-MAA-CIT (at 48 h) and FIB-MAA (at 24 h) led to increased mRNA expression and protein expression of PAD2 (p < 0.001) with increased protein citrullination.

CONCLUSION

These findings suggest that MAA-modification and citrullination of FIB, in isolation or combination, yield specific effects on macrophage polarization, PAD expression and citrullination that ultimately may induce inflammatory and fibrotic responses associated with RA.

Angiogenesis during coronal pulp regeneration using rat dental pulp cells: Neovascularization in rat molars in vivo and proangiogenic dental pulp cell-endothelial cell interactions in vitro

Background/purpose

Angiogenesis is considered a crucial event for dental pulp regeneration. The purpose of this study was to demonstrate neovascularization during coronal pulp regeneration in rat molars using rat dental pulp cells (rDPCs) and to examine whether rDPC-endothelial cell interactions promote proangiogenic capacity in vitro.

Materials and methods

Maxillary first molars of Wistar rats (n = 42) were pulpotomized and rDPCs isolated from incisors were implanted with a porous poly (l-lactic acid) (PLLA) scaffold and hydrogel (Matrigel). After 3, 7, and 14 days, coronal pulp tissues were examined histologically and by nestin and CD146 immunohistochemistry. rDPCs and rat dermal microvascular endothelial cells (rDMECs) were cocultured for 4 days and vascular endothelial growth factor (VEGF) synthesis and angiogenic factor gene expression were determined by enzyme-linked immunosorbent assays and real-time polymerase chain reaction, respectively. Effects of cocultured medium on tube formation by rDMECs were also evaluated.

Results

Implantation of rDPC/PLLA/Matrigel induced coronal pulp regeneration with dentin bridge formation and arrangement of nestin-positive odontoblast-like cells at 14 days. PLLA/Matrigel without rDPCs did not induce pulp regeneration. CD146-positive blood vessels increased in density in the remaining pulp tissues at 3 and 7 days, and in the regenerated pulp tissue at 14 days. rDPC/DMEC coculture significantly promoted VEGF secretion and mRNA expression of nuclear factor-kappa B, angiogenic chemokine CXCL1, and chemokine receptor CXCR1. Cocultured medium significantly promoted tube formation.

Conclusion

Coronal pulp regeneration with rDPC/PLLA/Matrigel was accompanied by neovascularization. rDPC-rDMEC interactions may promote angiogenic activity represented by proangiogenic factor upregulation and tube formation in vitro.

Effect of Streptococcus mutans on surface-topography, microhardness, and mechanical properties of contemporary resin composites

OBJECTIVE

Dental caries is the most prevalent disease globally, and Streptococcus mutans (S. mutans) is a common associated oral bacteria. Additionally, S. mutans possess esterase activity capable of degrading resin composites (RC). However, the effect of degradation on the physical-mechanical properties of the RC has not been extensively studied. We evaluated the flexure strength (FS), the diametral tensile strength (DTS), the modulus of elasticity (ME), and the microhardness of three contemporary RC to establish if S. mutans could affect them.

METHODS

One hundred thirty-eight bar-shaped and 276 disc-shaped specimens were fabricated with Enamel Plus HRi, IPS Empress Direct, and Clearfil AP-X, and physical-mechanical testing was done after been incubated during 30 and 60 days in culture media with or without S. mutans. Also, a scanning electron microscope was used to identify surface changes.

RESULTS

None of the tested RC were affected in their mechanical properties (FS, ME, and DTS). However, Clearfil AP-X and Enamel Plus HRI showed eroded surfaces and a decreased microhardness after 30 and 60 days S. mutans incubation. IPS Empress Direct presented the lowest values in all the tests, but its physical-mechanical features and surface were not affected by bacteria's exposure.

CONCLUSIONS

Exposure to S. mutans could affect some contemporary RC; however, the effect seems superficial since its mechanical features were not affected.

Polarization of macrophages in the trigeminal ganglion of rats with pulpitis

BACKGROUND

Dental pulp tissues are rich in pain-related afferent nerve fibers, which originate from primary sensory neurons in the trigeminal ganglion (TG). The mechanisms of central nervous system (CNS) underlying ectopic pain following peripheral inflammation have been reported that the macrophages as inflammatory and immunologic mediators in the TG play an important role in the process of pulpitis and hyperalgesia.

OBJECTIVE(S)

To observe the polarization response and dynamic distribution of macrophages in the TG during the development of dental pulp inflammation.

METHODS

A rat model of pulpitis was established using complete Freund's adjuvant (CFA). Hematoxylin-eosin (HE), immunohistochemistry (IHC), immunofluorescence (IF), toluidine blue (TB) staining, and RT-qPCR were performed to observe the expression of macrophage-related factors in the TG.

RESULTS

The results of IHC staining showed that M2 macrophages labeled with CD206 were observed in the TG of both the control and CFA groups. The statistical analysis indicated that the number of CD206-positive macrophages in the TG increased significantly at 24 h after CFA-induced pulpitis, reached a peak at 2 weeks, and then returned to the normal level after 6 weeks. The ratio of M2/M1 in the CFA groups was significantly lower than that in the control group from 24 to 72 h, and this pattern was reversed at 2 weeks after CFA-induced pulpitis; then, the ratio increased significantly and was maintained at a high level for 4 weeks. RT-qPCR results showed that the expression of IL-10 in the TG increased significantly from 1 to 4 weeks after CFA-induced pulpitis.

CONCLUSION

The trend of M2 macrophages was opposite to that of M1 macrophages in the TG during the process of pulpitis induced by CFA, which is consistent with the expression of macrophage-related cytokines. Macrophage polarization in the TG may participate in the neuroinflammation response induced by dental pulpitis.

PRIASE 2021 guidelines for reporting animal studies in Endodontology: explanation and elaboration

Laws and ethics require that before conducting human clinical trials, a new material, device or drug may have to undergo testing in animals in order to minimize health risks to humans, unless suitable supporting grandfather data already exist. The Preferred Reporting Items for Animal Studies in Endodontology (PRIASE) 2021 guidelines were developed exclusively for the specialty of Endodontology by integrating and adapting the ARRIVE (Animals in Research: Reporting In Vivo Experiments) guidelines and the Clinical and Laboratory Images in Publications (CLIP) principles using a validated consensus-based methodology. Implementation of the PRIASE 2021 guidelines will reduce potential sources of bias and thus improve the quality, accuracy, reproducibility, completeness and transparency of reports describing animal studies in Endodontology. The PRIASE 2021 guidelines consist of a checklist with 11 domains and 43 individual items and a flowchart. The aim of the current document is to provide an explanation for each item in the PRIASE 2021 checklist and flowchart and is supplemented with examples from the literature in order for readers to understand their significance and to provide usage guidance. A link to the PRIASE 2021 explanation and elaboration document and PRIASE 2021 checklist and flowchart is available on the Preferred Reporting Items for study Designs in Endodontology (PRIDE) website (http://pride-endodonticguidelines.org/priase/).

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

MicroRNA-enriched small extracellular vesicles possess odonto-immunomodulatory properties for modulating the immune response of macrophages and promoting odontogenesis

Background

To investigate the odonto-immunomodulatory properties of dental pulp stem cell-derived small extracellular vesicles (DPSCs-sEV), which promote odontogenesis by switching macrophages toward the pro-healing M2 phenotype.

Methods

MicroRNA sequencing was carried out for microRNA profiling of DPSCs-sEV. Automated Western blot, qPCR, ELISA, and flow cytometry were performed to identify the functions of microRNA-enriched DPSCs-sEV in macrophages. A luciferase reporter gene assay was carried out to confirm exosomal miR-125a-3p’s direct target gene. DPSCs-sEV-stimulated macrophage-conditioned media were used to promote odontogenesis in DPSCs and explore the mechanism of immune response in DPSCs-SEV-stimulated odontogenesis. DPSCs-sEV were injected into the exposed pulp tissue of rat incisor to investigate the odonto-immunomodulatory properties of DPSCs-sEV in vivo.

Results

DPSCs-sEV switched macrophages to the pro-healing M2 phenotype by inhibiting TLR and NFκΒ signaling. MicroRNA sequencing found 81 microRNAs significantly altered in DPSCS-sEV, with miR-125a-3p showing a 12-fold upregulation. Exosomal miR-125a-3p switched macrophages toward the M2 phenotype via inhibiting NFκΒ and TLR signaling via direct IKBKB targeting. Interestingly, DPSCs-sEV and the encapsulated miR-125a-3p enhanced BMP2 release in macrophages, promoting odontogenesis in DPSCs through BMP2 pathway activation. The rat study confirmed that DPSCs-sEV could be used as ideal biomimetic tools to enhance odontogenesis by switching macrophages toward pro-healing M2 cells.

Conclusions

We firstly defined the odonto-immunomodulatory properties of microRNA-enriched DPSCs-sEV, which could be used as ideal biomimetic tools to enhance odontogenesis by switching macrophages toward the pro-healing M2 phenotype.

Role of the CXCR4-SDF1-HMGB1 pathway in the directional migration of cells and regeneration of affected organs

In recent years, several studies have reported positive outcomes of cell-based therapies despite insufficient engraftment of transplanted cells. These findings have created a huge interest in the regenerative potential of paracrine factors released from transplanted stem or progenitor cells. Interestingly, this notion has also led scientists to question the role of proteins in the secretome produced by cells, tissues or organisms under certain conditions or at a particular time of regenerative therapy. Further studies have revealed that the secretomes derived from different cell types contain paracrine factors that could help to prevent apoptosis and induce proliferation of cells residing within the tissues of affected organs. This could also facilitate the migration of immune, progenitor and stem cells within the body to the site of inflammation. Of these different paracrine factors present within the secretome, researchers have given proper consideration to stromal cell-derived factor-1 (SDF1) that plays a vital role in tissue-specific migration of the cells needed for regeneration. Recently researchers recognized that SDF1 could facilitate site-specific migration of cells by regulating SDF1-CXCR4 and/or HMGB1-SDF1-CXCR4 pathways which is vital for tissue regeneration. Hence in this study, we have attempted to describe the role of different types of cells within the body in facilitating regeneration while emphasizing the HMGB1-SDF1-CXCR4 pathway that orchestrates the migration of cells to the site where regeneration is needed.

M2 Macrophages Enhance the Cementoblastic Differentiation of Periodontal Ligament Stem Cells via the Akt and JNK Pathways

Although macrophage (Mφ) polarization has been demonstrated to play crucial roles in cellular osteogenesis across the cascade of events in periodontal regeneration, how polarized Mφ phenotypes influence the cementoblastic differentiation of periodontal ligament stem cells (PDLSCs) remains unknown. In the present study, human monocyte leukemic cells (THP-1) were induced into M0, M1, and M2 subsets, and the influences of these polarized Mφs on the cementoblastic differentiation of PDLSCs were assessed in both conditioned medium-based and Transwell-based coculture systems. Furthermore, the potential pathways and cyto-/chemokines involved in Mφ-mediated cementoblastic differentiation were screened and identified. In both systems, M2 subsets increased cementoblastic differentiation-related gene/protein expression levels in cocultured PDLSCs, induced more PDLSCs to differentiate into polygonal and square cells, and enhanced alkaline phosphatase activity in PDLSCs. Furthermore, Akt and c-Jun N-terminal Kinase (JNK) signaling was identified as a potential pathway involved in M2 Mφ-enhanced PDLSC cementoblastic differentiation, and cyto-/chemokines (interleukin (IL)-10 and vascular endothelial growth factor [VEGF]) secreted by M2 Mφs were found to be key players that promoted cell cementoblastic differentiation by activating Akt signaling. Our data indicate for the first time that Mφs are key modulators during PDLSC cementoblastic differentiation and are hence very important for the regeneration of multiple periodontal tissues, including the cementum. Although the Akt and JNK pathways are involved in M2 Mφ-enhanced cementoblastic differentiation, only the Akt pathway can be activated via a cyto-/chemokine-associated mechanism, suggesting that players other than cyto-/chemokines also participate in the M2-mediated cementoblastic differentiation of PDLSCs. Stem Cells 2019;37:1567-1580.

In vivo fate of bone marrow mesenchymal stem cells implanted into rat pulpotomized molars

In our previous work, we established an in vivo coronal pulp regeneration model in which biodegradable hydrogel-made scaffolds carrying rat bone marrow mesenchymal stem cells (BM-MSCs) were implanted in the coronal pulp chamber of pulpotomized rat maxillary first molars. In this study, we investigated the in vivo fate of LacZ-labeled BM-MSCs in our coronal pulp regeneration model. BM-MSCs were nucleofected with pVectOZ-LacZ plasmid encoding β-galactosidase 1 day before implantation, and the LacZ-transfected BM-MSCs were implanted into the pulpotomized pulp chamber with biodegradable preformed scaffold-hydrogel constructs. Empty vector was used as a control. After 3 and 14 days, the molars were retrieved and subjected to β-galactosidase staining. At 3 days, β-galactosidase-expressing cells with a round profile were located mainly around the scaffold. At 14 days, when the pulp-like tissue had been generated, the majority of β-galactosidase-expressing cells were detected under the newly formed dentin bridge-like structure, where nestin-expressing odontoblast-like cells were arranged. Immunoreactivity for dentin sialoprotein, a marker of mature odontoblasts, was strongly detected under the original dentin. No β-galactosidase staining was observed in the control group. Thus, we demonstrated that BM-MSCs survived for 2 weeks after implantation and colonized within the site of potential cytodifferentiation. Our findings indicated that BM-MSCs could differentiate into cells involved in mineralized tissue formation in the functionally relevant region.