Therapeutic interaction of systemically-administered mesenchymal stem cells with peri-implant mucosa

CREB3L2 Regulates Hemidesmosome Formation during Epithelial Sealing

The long-term success rate of dental implants can be improved by establishing a favorable biological sealing with a high-quality epithelial attachment. The application of mesenchymal stem cells (MSCs) holds promise for facilitating the soft tissue integration around implants, but the molecular mechanism is still unclear and the general application of MSC sheet for soft tissue integration is also relatively unexplored. We found that gingival tissue-derived MSC (GMSC) sheet treatment significantly promoted the expression of hemidesmosome (HD)-related genes and proteins in gingival epithelial cells (GECs). The formation of HDs played a key role in strengthening peri-implant epithelium (PIE) sealing. Further, high-throughput transcriptome sequencing showed that GMSC sheet significantly upregulated the PI3K/AKT pathway, confirming that cell adhesion and HD expression in GECs were regulated by GMSC sheet. We observed that the expression of transcription factor CREB3L2 in GECs was downregulated. After treatment with PI3K pathway inhibitor LY294002, CREB3L2 messenger RNA and protein expression levels were upregulated. Further experiments showed that overexpression or knockdown of CREB3L2 could significantly inhibit or promote HD-related genes and proteins, respectively. We confirmed that CREB3L2 was a transcription factor downstream of the PI3K/AKT pathway and participated in the formation of HDs regulated by GMSC sheet. Finally, through the establishment of early implant placement model in rats, we clarified the molecular function of CREB3L2 in PIE sealing as a mechanical transmission molecule in GECs. The application of GMSC sheet-implant complex could enhance the formation of HDs at the implant-PIE interface and decrease the penetration distance of horseradish peroxidase between the implant and PIE. Meanwhile, GMSC sheet reduced the length of CREB3L2 protein expression on PIE. These findings elucidate the potential function and molecular mechanism of MSC sheet regulating the epithelial sealing around implants, providing new insights and ideas for the application of stem cell therapy in regenerative medicine.

Laminin 332-functionalized coating to regulate the behavior of keratinocytes and gingival mesenchymal stem cells to enhance implant soft tissue sealing

Peri-implant epithelial sealing is the first line of defense against external pathogens or stimuli; hence, an essential process to prevent peri-implantitis. Laminin 332 (LN332) is the main component of the internal basal lamina and participates in peri-implant epithelial sealing by forming hemidesmosomes (HDs) with integrin α6β4. In this work, poly (D, L-lactide) (PDLLA)-LN332 composite coating was successfully constructed by a method similar to layer-by-layer assembly, displaying staged LN332 release for as long as 28 days. The PDLLA-LN332 composite coating can activate the intracellular PI3K-Akt pathway via binding to cellular integrin α6β4, which can promote adhesion, migration and proliferation of HaCaT cells and further enhance the expression of keratinocyte HD-related molecules, including integrin α6β4, LN332 and plectin. Furthermore, the PDLLA-LN332 composite coating can promote the adhesion, spreading and proliferation of gingival mesenchymal stem cells and accelerate their epithelial differentiation. Therefore, the PDLLA-LN332 composite coating can enhance implant soft tissue sealing, warranting further in vivo study.

Assessment of the Soft-Tissue Seal at the Interface between the Base of the Fixed Denture Pontic and the Oral Mucosa

Fixed dentures (bridges) are often selected as a treatment option for a defective prosthesis. In this study, we assess the contact condition between the base of the pontic and oral mucosa, and examine the effect of prosthetic preparation and material biocompatibility. The molars were removed and replaced with experimental implants with a free-end type bridge superstructure after one week. In Experiment 1, we assessed different types of prosthetic pre-treatment: (1) the untreated control group (Con: mucosa recovering from the tooth extraction); (2) the laser irradiation group (Las: mucosa recovering after the damage caused by a CO₂ laser); and (3) the tooth extraction group (Ext: mucosa recovering immediately after the teeth extraction). In Experiment 2, five materials (titanium, zirconia, porcelain, gold-platinum alloy, and self-curing resin) were placed at the base of the bridge pontic. Four weeks after the placement of the bridge, the mucosa adjacent to the pontic base was histologically analyzed. In Experiment 1, the Con and Las groups exhibited no formation of an epithelial sealing structure on the pontic base. In the Ext group, adherent epithelium was observed. In Experiment 2, the sealing properties at the pontic interface were superior for titanium and the zirconia compared with those made of porcelain or gold-platinum alloy. In the resin group, a clear delay in epithelial healing was observed.

An overview of international regulatory frameworks for mesenchymal stromal cell-based medicinal products: From laboratory to patient

Human mesenchymal stromal cells (hMSCs) are emerging as one of the most important cell types in advanced therapies and regenerative medicine due to their great therapeutic potential. The development of hMSC-based products focuses on the use of hMSCs as biological active substances, and they are considered medicinal products by the primary health agencies worldwide. Due to their regulatory status, the development of hMSC-based products is regulated by specific criteria that range from the design phase, nonclinical studies, clinical studies, to the final registration and approval. Patients should only be administered hMSC-based products within the framework of a clinical trial or after the product has obtained marketing authorization; in both cases, authorization by health authorities is usually required. Considering the above, this paper describes the current general regulatory requirements for hMSC-based products, by jurisdiction, to be implemented throughout their entire development process. These measures may provide support for researchers from both public and private entities and academia to optimize the development of these products and their subsequent marketing, thereby improving access to them by patients.

Epithelial and Connective Tissue Sealing around Titanium Implants with Various Typical Surface Finishes

Soft tissue barrier around a dental implant plays a crucial role in the success of dental implants because it protects underlying hard tissue structures. A number of surface alteration procedures of implants have been introduced to improve bone-implant contact, but there has been little research on the peri-implant soft tissue (PIS) seal. The present study focuses on the "biologic width" of epithelial and connective tissue seals around implants with various typical surface finishes by testing surfaces that have been machined (Ms), roughened by sandblasting and acid etching (Rs), treated hydrothermally with CaCl₂ (Cs), or anodized (As). Ms, Rs, and As techniques are commonly used to finish surfaces of commercially available dental implants. The Cs technique was reported to produce strong epithelial cell-titanium adhesion. For culture study, rat oral epithelial cells (OECs) and fibroblasts were cultured on Ms, Rs, Cs, and As titanium plates. There was less cell adherence of OECs and more collagen expression when cultured on Rs and As plates than when cultured on Ms and Cs plates. For the in vivo study, implants with Ms, Rs, Cs, and As surfaces were placed in the rats' oral cavity. Although the PIS structure was similar to that around natural teeth, a horseradish peroxide assay revealed that the sealing ability around the Ms and Rs implants was weaker than that around Cs implants. After 16 weeks, Rs implants exhibited peri-implant epithelial apical down-growth and had lost bone support. Thus, although a smooth surface (Ms and Cs) showed better epithelial attachment, rough surfaces (Rs and As) are more suitable for binding to the connective tissue. Strong epithelium-implant attachment seems to be a fundamental defense against foreign body penetration. Selecting suitable surfaces to ensure strong sealing is important for implant success.

Tissue Engineering: What is New?

Soft and hard tissue engineering has expanded the frontiers of oral/maxillofacial augmentation. Soft tissue grafting enhancements include improving flap prevascularization and using stem cells and other cells to create not only the graft, but also the vascularization and soft tissue scaffolding for the graft. Hard tissue grafts have been enhanced by osteoinductive factors, such as bone morphogenic proteins, that have allowed the elimination of harvesting autogenous bone and thus decrease the need for other surgical sites. Advancements in bone graft scaffolds have developed via seeding with stem cells and improvement of the silica/calcium/phosphate composite to improve graft characteristics and healing.

Epithelial sealing effectiveness against titanium or zirconia implants surface

The aims of implant treatment now involve not only restoration of mastication function, but also recovery of esthetics. Currently, zirconia is widely used as an esthetic material for implant abutment. Therefore, it is very important to understand the efficacy of zirconia for epithelial sealing as an implant material. We compared the effects of materials on the sealing of the peri-implant epithelium (PIE) to titanium (Ti) or zirconia (Zr) implants, for application to clinical work. Maxillary first molars were extracted from rats and replaced with Ti or Zr implants. The sealing of the PIE to the implants was evaluated with immunohistochemistry observation and HRP analysis. The morphological and functional changes in rat oral epithelial cells (OECs) cultured on Ti or Zr plates were also evaluated. After 4 weeks, the PIE on the Ti and Zr implants showed similar structures. The Zr implants appeared to form a weak epithelial seal at the tissue-implant interface, and exhibited markedly less adhesive structures than the Ti implants under electron microscopic observation. In the in vitro experiments, decreased expression levels of adhesion proteins were observed in OECs cultured on Zr plates compared with those cultured on Ti plates. In addition, the cell adherence on Zr plates was reduced, while the cell migration was low on Ti plates. Zr is a better choice for an esthetic implant material, but needs further improvement for integration with the epithelial wound healing process around a dental implant. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

The influence of systemically or locally administered mesenchymal stem cells on tissue repair in a rat oral implantation model

BACKGROUND

Multipotent mesenchymal stem cells (MSCs) are used clinically in regenerative medicine. Our previous report showed systemically injected MSCs improved peri-implant sealing and accelerated tissue healing. However, the risks of systemic MSC administration, including lung embolism, must be considered; therefore, their local application must be assessed for clinical safety and efficacy. We investigated differences in treatment effect between local and systemic MSC application using a rat oral implantation model.

METHODS

Rat bone marrow-derived MSCs were isolated and culture-expanded. The rat's right maxillary first molars were extracted and replaced with experimental titanium implants. After 24 h, MSCs (1 × 106/ml) were systemically or locally injected into recipient rats via the tail vein (systemic group) or buccal subcutaneous tissue (local group), respectively. Rats treated in the absence of MSCs were included as a control (control group). The maxillary epithelium was assessed histologically after 4 weeks to evaluate laminin-332 (Ln-332) distribution and horseradish peroxidase invasion, as indicators of peri-implant epithelium (PIE) formation and PIE sealing to the implant surface, respectively. The effect of MSCs on rat oral epithelial cell (OEC) morphology was determined by coculture.

RESULTS

Systemic group MSCs accumulated early at the peri-implant mucosa, while local group MSCs were observed in various organs prior to later accumulation around the implant surface. PIE formation and Ln-332-positive staining at the implant interface were enhanced in the systemic group compared with the local and control groups. Furthermore, OEC adherence on implants was reduced in high-density compared with low-density MSC cocultures.

CONCLUSIONS

Local MSC injection was more ineffective than systemic MSC injection at enhancing PIE sealing around titanium implants. Thus, although local MSC administration has a wide range of applications, further investigations are needed to understand the exact cellular and molecular mechanisms of this approach prior to clinical use.

Enamel matrix derivative enhances the proliferation and osteogenic differentiation of human periodontal ligament stem cells on the titanium implant surface

Periodontal ligament stem cells (PDLSCs) have mesenchymal-stem-cells-like qualities, and are considered as one of the candidates of future clinical application in periodontal regeneration therapy. Enamel matrix derivative (EMD) is widely used in promoting periodontal regeneration. However, the effects of EMD on the proliferation and osteogenic differentiation of human PDLSCs grown on the Ti implant surface are still no clear. Therefore, this study examined the effects of EMD on human PDLSCs in vitro. Human PDLSCs were isolated from healthy participants, and seeded on the surface of Ti implant disks and stimulated with various concentrations of EMD. Cell proliferation was determined with Cell Counting Kit-8 (CCK-8). The osteogenic differentiation of PDLSCs was evaluated by the measurement of alkaline phosphatase (ALP) activity, Alizarin red staining, and real-time polymerase chain reaction (qRT-PCR) and Western blotting, respectively. The results indicated that EMD at concentrations (5-60 µg/ml) increased the viability and proliferation of PDLSCs. The treatment with 30 and 60 µg/ml of EMD significantly elevated ALP activity, augmented mineralized nodule formation and calcium deposition, and upregulated the mRNA and protein levels of Runx-2 and osteocalcin (OCN) in the PDLSCs grown on the Ti surface. Further investigation found that EMD treatment did not change the protein levels of phosphatidylinositol-3-kinase (PI3K), p-PI3K, Akt and mTOR, but significantly upregulated the phosphorylated levels of Akt and mTOR. Collectively, these results suggest that EMD stimulation can promote the proliferation and osteogenic differentiation of PDLSCs grown on Ti surface, which is possibly associated with the activation of Akt/mTOR signaling pathway.

Therapeutic interactions between mesenchymal stem cells for healing medication-related osteonecrosis of the jaw

Background

Mesenchymal stem cells (MSCs) have been isolated from a variety of tissues, including bone marrow, adipose, and mucosa. MSCs have the capacity for self-renewal and differentiation. Reports have been published on the systemic administration of MSCs leading to functional improvements by engraftment and differentiation, thus providing a new strategy to regenerate damaged tissues. Recently, it has become clear that MSCs possess immunomodulatory properties and can therefore be used to treat diseases. However, the therapeutic effect mechanisms of MSCs are yet to be determined. Here, we investigated these mechanisms using a medication-related osteonecrosis of the jaw (MRONJ)-like mouse model.

Methods

To generate MRONJ-like characteristics, mice received intravenous zoledronate and dexamethasone two times a week. At 1 week after intravenous injection, maxillary first molars were extracted, and at 1 week after tooth extraction, MSCs were isolated from the bone marrow of the mice femurs and tibias. To compare “diseased MSCs” from MRONJ-like mice (d-MSCs) with “control MSCs” from untreated mice (c-MSCs), the isolated MSCs were analyzed by differentiation and colony-forming unit-fibroblast (CFU-F) assays and systemic transplantation of either d-MSCs or c-MSCs into MRONJ-like mice. Furthermore, we observed the exchange of cell contents among d-MSCs and c-MSCs during coculture with all combinations of each MSC type.

Results

d-MSCs were inferior to c-MSCs in differentiation and CFU-F assays. Moreover, the d-MSC-treated group did not show earlier healing in MRONJ-like mice. In cocultures with any combination, MSC pairs formed cell–cell contacts and exchanged cell contents. Interestingly, the exchange among c-MSCs and d-MSCs was more frequently observed than other pairs, and d-MSCs were distinguishable from c-MSCs.

Conclusions

The interaction of c-MSCs and d-MSCs, including exchange of cell contents, contributes to the treatment potential of d-MSCs. This cellular behavior might be one therapeutic mechanism used by MSCs for MRONJ.