The Antimicrobial Peptide LL-37 Promotes Migration and Odonto/Osteogenic Differentiation of Stem Cells from the Apical Papilla through the Akt/Wnt/β-catenin Signaling Pathway

Harnessing antimicrobial peptides in endodontics

Endodontic therapy includes various procedures such as vital pulp therapy, root canal treatment and retreatment, surgical endodontic treatment and regenerative endodontic procedures. Disinfection and tissue repair are crucial for the success of these therapies, necessitating the development of therapeutics that can effectively target microbiota, eliminate biofilms, modulate inflammation and promote tissue repair. However, no current endodontic agents can achieve these goals. Antimicrobial peptides (AMPs), which are sequences of amino acids, have gained attention due to their unique advantages, including reduced susceptibility to drug resistance, broad-spectrum antibacterial properties and the ability to modulate the immune response of the organism effectively. This review systematically discusses the structure, mechanisms of action, novel designs and limitations of AMPs. Additionally, it highlights the efforts made by researchers to overcome peptide shortcomings and emphasizes the potential applications of AMPs in endodontic treatments.

The Current Progress of Tetrahedral DNA Nanostructure for Antibacterial Application and Bone Tissue Regeneration

Recently, programmable assembly technologies have enabled the application of DNA in the creation of new nanomaterials with unprecedented functionality. One of the most common DNA nanostructures is the tetrahedral DNA nanostructure (TDN), which has attracted great interest worldwide due to its high stability, simple assembly procedure, high predictability, perfect programmability, and excellent biocompatibility. The unique spatial structure of TDN allows it to penetrate cell membranes in abundance and regulate cellular biological properties as a natural genetic material. Previous studies have demonstrated that TDNs can regulate various cellular biological properties, including promoting cells proliferation, migration and differentiation, inhibiting cells apoptosis, as well as possessing anti-inflammation and immunomodulatory capabilities. Furthermore, functional molecules can be easily modified at the vertices of DNA tetrahedron, DNA double helix structure, DNA tetrahedral arms or DNA tetrahedral cage structure, enabling TDN to be used as a nanocarrier for a variety of biological applications, including targeted therapies, molecular diagnosis, biosensing, antibacterial treatment, antitumor strategies, and tissue regeneration. In this review, we mainly focus on the current progress of TDN-based nanomaterials for antimicrobial applications, bone and cartilage tissue repair and regeneration. The synthesis and characterization of TDN, as well as the biological merits are introduced. In addition, the challenges and prospects of TDN-based nanomaterials are also discussed.

Role of CPNE1 in Odontoblastic Differentiation of Rat Stem Cells from Apical Papilla

CPNE1 is a calcium-dependent, phospholipid-binding protein that is ubiquitously expressed in various tissues and organs. This study investigates the expression and localization of CPNE1 in tooth germ development and the role of CPNE1 in odontoblastic differentiation. In rat tooth germs, CPNE1 is expressed in the odontoblasts and ameloblasts since the late bell stage. The depletion of CPNE1 in the stem cells from apical papilla (SCAPs) clearly inhibits the expression of odontoblastic-related genes and the formation of mineralized nodules during differentiation, while CPNE1 overexpression promotes this process. In addition, CPNE1 overexpression increases AKT phosphorylation during the odontoblastic differentiation of SCAPs. Furthermore, treatment with AKT inhibitor (MK2206) reduces the expression of odontoblastic-related genes in CPNE1 over-expressed SCAPs, and Alizarin Red staining shows reduced mineralization. These results suggest that CPNE1 plays a role in the tooth germ development as well as the odontblastic differentiation of SCAPs in vitro that is related to the AKT signaling pathway.

Regulation of LL-37 in Bone and Periodontium Regeneration

The goal of regenerative therapy is to restore the structure and function of the lost tissues in the fields of medicine and dentistry. However, there are some challenges in regeneration therapy such as the delivery of oxygen and nutrition, and the risk of infection in conditions such as periodontitis, osteomyelitis, etc. Leucine leucine-37 (LL-37) is a 37-residue, amphipathic, and helical peptide found only in humans and is expressed throughout the body. It has been shown to induce neovascularization and vascular endothelial growth factor (VEGF) expression. LL-37 also stimulates the migration and differentiation of mesenchymal stem cells (MSCs). Recent studies have shown that LL-37 plays an important role in the innate defense system through the elimination of pathogenic microbes and the modulation of the host immune response. LL-37 also manifests other functions such as promoting wound healing, angiogenesis, cell differentiation, and modulating apoptosis. This review summarizes the current studies on the structure, expression, and function of LL-37 and highlights the contributions of LL-37 to oral cavity, periodontium, and bone regeneration.

Cathelicidin LL-37 improves bone metabolic balance in rats with ovariectomy-induced osteoporosis via the Wnt/beta-catenin pathway

Osteoporosis is a bone disease characterized by low bone mineral density (BMD) and impaired bone microarchitecture due to the abnormal activity of osteoclasts. Cathelicidins are antimicrobial peptides present in the lysosomes of macrophages and polymorphonuclear leukocytes. LL-37, a cathelicidin, induces various biological effects, including modulation of the immune system, angiogenesis, wound healing, cancer growth, as well as inflammation, and bone loss. A previous study reported direct involvement of LL-37 suppressing osteoclastogenesis in humans. Here, we examined the role of LL-37 in the treatment of osteoporosis using an ovariectomy (OVX) rat model. Our results showed that LL-37 significantly reduced bone loss and pathological injury in OVX rats with osteoporosis. Furthermore, we found that LL-37 significantly increased the activity of the Wnt/beta-catenin pathway in OVX rats with osteoporosis, including the increased expression of beta-catenin, Osterix (Osx), and Runt-related transcription factor 2 (Runx2), whereas XAV-939, an inhibitor of the Wnt/beta-catenin pathway, significantly blocked the effects of LL-37 on bone loss and abnormal bone metabolism. Altogether, our findings suggested that LL-37 exerted a protective role in regulating bone loss and abnormal bone metabolism in rats with osteoporosis by activating the Wnt/beta-catenin pathway.

Cathelicidin LL-37 in Health and Diseases of the Oral Cavity

The mechanisms for maintaining oral cavity homeostasis are subject to the constant influence of many environmental factors, including various chemicals and microorganisms. Most of them act directly on the oral mucosa, which is the mechanical and immune barrier of the oral cavity, and such interaction might lead to the development of various oral pathologies and systemic diseases. Two important players in maintaining oral health or developing oral pathology are the oral microbiota and various immune molecules that are involved in controlling its quantitative and qualitative composition. The LL-37 peptide is an important molecule that upon release from human cathelicidin (hCAP-18) can directly perform antimicrobial action after insertion into surface structures of microorganisms and immunomodulatory function as an agonist of different cell membrane receptors. Oral LL-37 expression is an important factor in oral homeostasis that maintains the physiological microbiota but is also involved in the development of oral dysbiosis, infectious diseases (including viral, bacterial, and fungal infections), autoimmune diseases, and oral carcinomas. This peptide has also been proposed as a marker of inflammation severity and treatment outcome.

Enhanced Antibacterial Ability and Bioactivity of Polyetherketoneketone Modified with LL-37

Polyetherketoneketone (PEKK) is considered to be a potential substitute material for metal bone implants because of its advantageous biocompatibility, chemical stability, and mechanical properties, but clinical application has been severely restricted due to PEKK's lack of antibacterial ability and biological activity. In this study, LL-37, a natural human antimicrobial peptide, was successfully modified on the PEKK surface with polydopamine as the intermediate layer and released continuously for more than 6 days. The results of the MTT assay, colony counts, and Live/Dead staining demonstrated that compared to unmodified PEKK, the LL-37-modified PEKK significantly inhibited the adhesion, vitality, and bacterial biofilm growth of Staphylococcus aureus and Escherichia coli in a concentration-dependent way. Furthermore, the LL-37-modified PEKK enhanced biocompatibility (cell adhesion and viability) and promoted osteogenic differentiation of human umbilical cord Wharton's jelly-derived mesenchymal stem cells. Our data suggested that LL-37-modified PEKK might be a promising material for use in orthopedic implants.

miR-342-5p inhibits odonto/osteogenic differentiation of human dental pulp stem cells via targeting Wnt7b

OBJECTIVE

Human dental pulp stem cells (hDPSCs) constitute a promising source of stem cells in tissue engineering. However, the molecular mechanism of differentiation in hDPSCs remains largely unclear. MicroRNAs (miRNAs) play crucial roles in lineage-specific differentiation of stem cells. The present study investigated the function of miRNA-342-5p in the odonto/osteogenic differentiation of hDPSCs.

METHODS

The miRNA array profiling and quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) revealed the expression of miR-342-5p during odonto/osteogenic differentiation of hDPSCs. hDPSCs were treated with miR-342-5p mimic and inhibitor to investigate the regulatory roles of miR-342-5p in the differentiation of hDPSCs. Moreover, miR-342-5p inhibitor and small interference RNA (siRNA) targeting Wnt7b were applied to explore the regulatory mechanism of miR-342-5p.

RESULTS

Downregulated miR-342-5p was observed during odonto/osteogenic differentiation of hDPSCs. The overexpression of miR-342-5p inhibited the odonto/osteogenic potential of DPSCs, as indicated by low levels of alkaline phosphatase activity, calcium deposition formation, and odonto/osteogenic differentiation markers, whereas silencing of miR-342-5p exhibited the opposite effect. When co-treated with siRNA targeting Wnt7b and miR-342-5p inhibitor in hDPSCs, the odonto/osteogenic potential and activation of Wnt7b/β-catenin pathway were attenuated.

CONCLUSIONS

This study showed that miR-342-5p inhibits the odonto/osteogenic differentiation of hDPSCs by interfering with Wnt/β-catenin signaling via targeting Wnt7b.

Immunomodulatory Expression of Cathelicidins Peptides in Pulp Inflammation and Regeneration: An Update

The role of inflammatory mediators in dental pulp is unique. The local environment of pulp responds to any changes in the physiology that are highly fundamental, like odontoblast cell differentiation and other secretory activity. The aim of this review is to assess the role of cathelicidins based on their capacity to heal wounds, their immunomodulatory potential, and their ability to stimulate cytokine production and stimulate immune-inflammatory response in pulp and periapex. Accessible electronic databases were searched to find studies reporting the role of cathelicidins in pulpal inflammation and regeneration published between September 2010 and September 2020. The search was performed using the following databases: Medline, Scopus, Web of Science, SciELO and PubMed. The electronic search was performed using the combination of keywords "cathelicidins" and "dental pulp inflammation". On the basis of previous studies, it can be inferred that LL-37 plays an important role in odontoblastic cell differentiation and stimulation of antimicrobial peptides. Furthermore, based on these outcomes, it can be concluded that LL-37 plays an important role in reparative dentin formation and provides signaling for defense by activating the innate immune system.