Periodontal regeneration with autologous periodontal ligament-derived cell sheets - A safety and efficacy study in ten patients

Mass acquisition of human periodontal ligament stem cells

The periodontal ligament (PDL) is an essential fibrous tissue for tooth retention in the alveolar bone socket. PDL tissue further functions to cushion occlusal force, maintain alveolar bone height, allow orthodontic tooth movement, and connect tooth roots with bone. Severe periodontitis, deep caries, and trauma cause irreversible damage to this tissue, eventually leading to tooth loss through the destruction of tooth retention. Many patients suffer from these diseases worldwide, and its prevalence increases with age. To address this issue, regenerative medicine for damaged PDL tissue as well as the surrounding tissues has been extensively investigated regarding the potential and effectiveness of stem cells, scaffolds, and cytokines as well as their combined applications. In particular, PDL stem cells (PDLSCs) have been well studied. In this review, I discuss comprehensive studies on PDLSCs performed in vivo and contemporary reports focusing on the acquisition of large numbers of PDLSCs for therapeutic applications because of the very small number of PDLSCs available in vivo.

Tissue engineering using a combined cell sheet technology and scaffolding approach

Cell sheet technology has remained quite popular among tissue engineering techniques over the last several years. Meanwhile, there is an apparent trend in modern scientific research towards combining different approaches and strategies. Accordingly, a large body of work has arisen where cell sheets are used not as separate structures, but in combination with scaffolds as supporting constructions. The aim of this review is to analyze the intersection of these two vast areas of tissue engineering described in the literature mainly within the last five years. Some practical and technical details are emphasized to provide information that can be useful in research design and planning. The first part of the paper describes the general issues concerning the use of combined technology, its advantages and limitations in comparison with those of other tissue engineering approaches. Next, the detailed literature analysis of in vivo studies aimed at the regeneration of different tissues is performed. A significant part of this section concerns bone regeneration. In addition to that, other connective tissue structures, including articular cartilage and fibrocartilage, ligaments and tendons, and some soft tissues are discussed. STATEMENT OF SIGNIFICANCE: This paper describes the intersection of two technologies used in designing of tissue-engineered constructions for regenerative medicine: cell sheets as extracellular matrix-rich structures and supporting scaffolds as essentials in tissue engineering. A large number of reviews are devoted to each of these scientific problems. However, the solution of complex problems of tissue engineering requires an integrated approach that includes both three-dimensional scaffolds and cell sheets. This manuscript serves as a description of advantages and limitations of this method, its use in regeneration of bones, connective tissues and soft tissues and some other details.

Decellularized human corneal stromal cell sheet as a novel matrix for ocular surface reconstruction

The shortage of donor corneas as well as the limitations of tissue substitutes leads to the necessity to develop alternative materials for ocular surface reconstruction. Corneal surface substitutes must fulfill specific requirements such as high transparency, low immunogenicity, and mechanical stability combined with elasticity. This in vitro study evaluates a decellularized matrix secreted from human corneal fibroblasts (HCF) as an alternative material for ocular surface reconstruction. HCF from human donors were cultivated with the supplementation of vitamin C to form a stable and thick matrix. Furthermore, due to enhanced cultivation time, a three-dimensional like multilayered construct which partly mimics the complex structure of the corneal stroma could be generated. The formed human cell-based matrices (so-called cell sheets [CS]) were subsequently decellularized. The complete cell removal, collagen content, ultrastructure, and cell toxicity of the decellularized CS (DCS) as well as biomechanical properties were analyzed. Surgical feasibility was tested on enucleated porcine eyes. After decellularization and sterilization, a transparent, thick, cell free, and sterile tissue substitute resulted, which allowed expansion of limbal epithelial stem cells with no signs of cytotoxicity, and good surgical feasibility. DCS seem to be a promising new corneal tissue substitute derived from human cells without the limitation of donor material; however, future in vivo studies are necessary to further elucidate its potential for ocular surface reconstruction.

Attenuated regenerative properties in human periodontal ligament-derived stem cells of older donor ages with shorter telomere length and lower SSEA4 expression

Periodontal ligament (PDL) stem cell properties are critical in the periodontal tissue regeneration for periodontitis. Previously, we have demonstrated that cigarette smoking attenuates PDL-derived stem cell (PDLSC) regenerative properties. Here, we report the findings on the regenerative properties of human PDLSCs with different donor ages and the underlying mechanisms. Human PDLSCs from 18 independent donors were divided into different age groups (≤ 20, 20-40, and > 40 years old). The proliferation of PDLSCs with donor age of ≤ 20 years old was significantly higher than that of the 20-40- and > 40-years-old groups, whereas the migration of PDLSCs with donor age of ≤ 20 and 20-40 years old was significantly higher than that of the > 40-years-old group. Moreover, the mesodermal lineage differentiation capabilities of PDLSCs were also higher in the donor age group of ≤ 20 years old than the donor age of > 40 years old. In addition, shorter telomere length and lower expression of SSEA4 were found in PDLSCs with donor age of > 40 years old, compared with those with donor age of ≤ 20-years-old group. Besides, PDLSCs with donor age of 20-40 and > 40 years old had higher IL6 and CXCL8 gene expressions. In summary, results from this study revealed the attenuated proliferation, migration, and mesodermal lineage differentiation properties in human PDLSCs with older donor ages. Donor age of PDLSCs should be considered as the selection criteria for the periodontal tissue regeneration treatment.

Periodontal Ligament Stem Cells: Regenerative Potency in Periodontium

Periodontium is consisted of root cementum, bone lining the tooth socket, gingiva facing the tooth, and periodontal ligament (PDL). Its primary functions are support of the tooth and protection of tooth, nerve, and blood vessels from injury by mechanical loading. Severe periodontitis induces the destruction of periodontium and results in a significant cause of tooth loss among adults. Unfortunately, conventional therapies such as scaling and root planning are often only palliative. Therefore, the ultimate goal of the treatment for periodontitis is to restore disrupted periodontium to its original shape and function. Tissue engineering refers to the process of combining cells, scaffolds, and signaling molecules for the production of functional tissues to restore, maintain, and improve damaged organs. The discovery of periodontal ligament stem cells (PDLSCs) highlighted the possibility for development of tissue engineering technology-based therapeutics for disrupted periodontium. PDLSCs are a kind of somatic stem cells that show potential to differentiate into multiple cell types and undergo robust clonal self-renewal. Therefore, PDLSCs are considered a highly promising stem cell population for regenerative therapy in periodontium; however, their rarity prevents the progression of basic and clinical researches. In this review, we summarize recent research advancement and accumulated information regarding the self-renewal capacity, multipotency, and immunomodulatory effect of PDLSCs, as well as their contribution to repair and regeneration of periodontium and other tissues. We also discuss the possibility of PDLSCs for clinical application of regenerative medicine and provide an outline of the genetic approaches to overcome the issue about the rarity of PDLSCs.

rhBMP-2 Pre-Treated Human Periodontal Ligament Stem Cell Sheets Regenerate a Mineralized Layer Mimicking Dental Cementum

The periodontal complex consisting of alveolar bone, cementum, and periodontal ligaments (PDL) supports human teeth through the systematic orchestration of mineralized tissues and fibrous tissues. Importantly, cementum, the outermost mineralized layer of dental roots, plays an essential role by bridging the inner ligaments from the dental root to the alveolar bone. When the periodontal complex is damaged, the regeneration of each component of the periodontal complex is necessary; however, it is still challenging to achieve complete functional regeneration. In this study, we tried to control the regeneration of cementum and PDL by using a human PDL stem cell (hPDLSC) sheet engineering technology with the pretreatment of recombinant human BMP-2 (rhBMP-2). Isolated hPDLSCs obtained from extracted human teeth were pretreated with rhBMP-2 for in vitro osteogenic differentiation and grafted on the micro/macro-porous biphasic calcium phosphate (MBCP) blocks, which represent dental roots. The MBCPs with hPDLSC sheets were implanted in the subcutaneous layer of immune-compromised mice, and rhBMP-2 pretreated hPDLSC sheets showed higher mineralization and collagen ligament deposition than the no-pretreatment group. Therefore, the rhBMP-2-hPDLSC sheet technique could be an effective strategy for the synchronized regeneration of two different tissues: mineralized tissue and fibrous tissues in periodontal complexes.

Promising advances in clinical trials of dental tissue-derived cell-based regenerative medicine

Background

Advances in regenerative medicine with stem cells have led to clinical trials. Dental/oral tissues are emerging as promising cellular sources of human mesenchymal stem cells. Recently, dental tissue-derived cells have been used clinically due to their great potential, easy accessibility, and ability to be obtained via methods with low invasiveness. The aim of this study is to systematically assess the clinical effectiveness of dental cell-mediated therapies compared to current evidence-based methods in human patients.

Methods

The electronic databases MEDLINE, Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrials.gov were searched up to December 2019 for clinical trials. Clinical trials with any intervention using stem cells/cells derived from dental tissue were included.

Results

A total of 815 studies were identified by the electronic search, and 38 articles qualified for full-text evaluation. Finally, 20 studies (10 clinical trials using dental pulp-derived cells, 3 clinical trials using periodontal ligament-derived cells, and 7 studies using gingiva-derived cells) were included in this review. No clinical trials using dental follicle- or apical papilla-derived cells were selected in this review. Dental pulp-derived cells were used in clinical trials for bone regeneration, periodontitis, and dental pulp regeneration. All clinical trials using periodontal ligament-derived cells and gingiva-derived cells were conducted for periodontal disease treatment and gingival augmentation, respectively. Among the 20 selected studies, 16 showed clinical benefits of cell transplantation therapies. In addition, no study reported adverse events that may have been associated with cell transplantation.

Conclusions

These findings indicate that dental tissue-derived cells would be useful for cell-based regenerative medicine for various diseases.

Construction of higher-order cellular microstructures by a self-wrapping co-culture strategy using a redox-responsive hydrogel

In this report, a strategy for constructing three-dimensional (3D) cellular architectures comprising viable cells is presented. The strategy uses a redox-responsive hydrogel that degrades under mild reductive conditions, and a confluent monolayer of cells (i.e., cell sheet) cultured on the hydrogel surface peels off and self-folds to wrap other cells. As a proof-of-concept, the self-folding of fibroblast cell sheet was triggered by immersion in aqueous cysteine, and this folding process was controlled by the cysteine concentration. Such folding enabled the wrapping of human hepatocellular carcinoma (HepG2) spheroids, human umbilical vein endothelial cells and collagen beads, and this process improved cell viability, the secretion of metabolites and the proliferation rate of the HepG2 cells when compared with a two-dimensional culture under the same conditions. A key concept of this study is the ability to interact with other neighbouring cells, providing a new, simple and fast method to generate higher-order cellular aggregates wherein different types of cellular components are added. We designated the method of using a cell sheet to wrap another cellular aggregate the 'cellular Furoshiki'. The simple self-wrapping Furoshiki technique provides an alternative approach to co-culture cells by microplate-based systems, especially for constructing heterogeneous 3D cellular microstructures.

Stable cell adhesion affects mesenchymal stem cell sheet fabrication: Effects of fetal bovine serum and human platelet lysate

Cell sheet technology exploits temperature responsive cell culture dishes (TRCDs) as versatile cell harvesting methods to yield contiguous cell monolayers robustly held together by cell-cell junctions, receptors, and endogenous extracellular matrix. More than 15 years of clinical data using autologous-sourced cell sheets demonstrate enhanced therapeutic properties through increased cell retention at target tissue sites. Recently, several preclinical studies have also been reported using mesenchymal stem cell (MSC) sheets in wound healing, cardiac ischemia therapies, and pancreatic regeneration. However, optimized MSC sheet fabrication conditions have not yet been reported. In this study, we identified specific conditions for reliable human MSC sheet fabrication by comparing cell growth media supplements (fetal bovine serum [FBS] and human platelet lysate [hPL]). Human umbilical cord-derived MSCs cultured in FBS and hPL exhibit different actin cytoskeletal structures related to their cell morphologies and adhesion. MSCs cultured in FBS media showed stable cell adhesion on TRCDs with flattened cell shapes and aligned actin cytoskeletal structure. This stable cell adhesion enables production of consistent MSC cell sheets, with controlled cell sheet detachment. Conversely, cell sheet fabrication in hPL media exhibits poor reproducibility being more sensitive to temperature- and culture time-induced release due to weak cell adhesion. These findings suggest that stable MSC adhesion to TRCDs is important to reliable MSC sheet fabrication methods and that MSC growth media supplementation directly affects cell adhesion during culture.

Three-dimensional periodontal tissue regeneration using a bone-ligament complex cell sheet

Periodontal tissue is a distinctive tissue structure composed three-dimensionally of cementum, periodontal ligament (PDL) and alveolar bone. Severe periodontal diseases cause fundamental problems for oral function and general health, and conventional dental treatments are insufficient for healing to healthy periodontal tissue. Cell sheet technology has been used in many tissue regenerations, including periodontal tissue, to transplant appropriate stem/progenitor cells for tissue regeneration of a target site as a uniform tissue. However, it is still difficult to construct a three-dimensional structure of complex tissue composed of multiple types of cells, and the transplantation of a single cell sheet cannot sufficiently regenerate a large-scale tissue injury. Here, we fabricated a three-dimensional complex cell sheet composed of a bone-ligament structure by layering PDL cells and osteoblast-like cells on a temperature responsive culture dish. Following ectopic and orthotopic transplantation, only the complex cell sheet group was demonstrated to anatomically regenerate the bone-ligament structure along with the functional connection of PDL-like fibers to the tooth root and alveolar bone. This study represents successful three-dimensional tissue regeneration of a large-scale tissue injury using a bioengineered tissue designed to simulate the anatomical structure.

Cell sheet tissue engineering for scaffold-free three-dimensional (3D) tissue reconstruction

Three-dimensional (3D) reconstruction of highly functional tissues is of great importance in advancing the clinical benefit of tissue engineering and regenerative medicine. In the last quarter century, many studies have found that by engineering a 3D microenvironment that resembles the in vivo tissue condition, cells exhibit behaviors and functions that reflect those of native tissue. Biomaterial scaffolds are a central technology for providing 3D microenvironments in vitro, and, in conjunction with diverse design and cell seeding advents, have produced highly functional and complex 3D tissues. Here, we describe a new approach to creating 3D cell-dense tissue-like constructs without a biomaterial scaffold. Cell sheet technology with cell sheet layering strategies generates highly cell dense, engineered tissue capable of direct crosstalk with the tissue-engraftment surface, in addition to paracrine-mediated signaling. In this chapter, we will introduce methods of reconstructing 3D tissue using cell sheet technology and the advantages of a scaffold-free design.

Mesenchymal stem cell-based tissue regeneration therapies for periodontitis

Periodontitis is commonly observed and is an important concern in dental health. It is characterized by a multifactorial etiology, including imbalance of oral microbiota, mechanical stress, and systemic diseases such as diabetes mellitus. The current standard treatments for periodontitis include elimination of the microbial pathogen and application of biomaterials for treating bone defects. However, the periodontal tissue regeneration via a process consistent with the natural tissue formation process has not yet been achieved. Developmental biology studies state that periodontal tissue is composed of neural crest-derived ectomesenchyme. To elucidate the process of periodontal regeneration, it is essential to understand the developmental background and intercellular cross-talk. Several recent studies have reported the efficacy of transplantation of mesenchymal stem cells for periodontal tissue regeneration. In this review, we discuss the basic knowledge of periodontal tissue regeneration using mesenchymal stem cells and highlight the potential of stem cell-based periodontal regenerative medicine.

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Neural crest cells regulate the development and homeostasis of periodontal tissues.

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Dental mesenchymal stem cells (MSCs) are used for treating alveolar bone defects.

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Non-odontogenic MSCs can be investigated for periodontal tissue regeneration.

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Using appropriate growth factors and scaffold may improve periodontium regeneration.

Enhanced mechanical properties and cell separation with thermal control of PIPAAm-brushed polymer-blend microfibers

Thermoresponsive microfibers with enhanced mechanical properties for temperature-modulated cell separation were developed by electrospinning of blending PVBC and PBMA, and by subsequently modifying the microfibers with PIPAAm via ATRP.

Extracellular matrix derived from human urine-derived stem cells enhances the expansion, adhesion, spreading, and differentiation of human periodontal ligament stem cells

Background

Human periodontal ligament stem cells (hPDLSCs) are one of the most promising types of seed cells in periodontal tissue regeneration. Suitable biomaterials are additional essential components that must cooperate with seed cells for in vivo expansion or in vitro implantation. Extracellular matrix (ECM) derived from mesenchymal stem cells (MSCs) was recently reported to be a promising substrate with which to culture MSCs that could be applied in biomaterial scaffolds or bioink. Human urine-derived stem cells (hUSCs) have several advantages; their collection is non-invasive and easy, and hUSCs are low in cost, potentially making them a suitable and efficient source of ECM. The purpose of this study was to characterize the biological properties of ECM derived from hUSCs (UECM) and evaluate the effects of UECM on hPDLSCs.

Methods

hPDLSCs grown on ECM derived from hPDLSCs (PECM) and fibronectin-coated tissue culture plastic (TCP) served as control groups. Both hUSCs and hPDLSCs were seeded on TCP and stimulated to produce ECM. After 8 days of stimulation, the samples were decellularized, leaving only ECM. Then, hPDLSCs were seeded onto UECM-, PECM-, and fibronectin-coated TCP and untreated TCP.

Results

UECM consists of dense bundles of fibers which contain abundant fibronectin. Both UECM and PECM promoted hPDLSC proliferation, attachment, spreading, and differentiation. Between UECM and PECM, UECM enhanced proliferation, osteogenesis, and angiogenesis to a greater extent. Though fibronectin appeared to be the abundant component of UECM, its performance was inferior to that of UECM.

Conclusions

Our study provides an original perspective on different cell-specific ECMs and suggests UECM as a suitable biomaterial in which to culture hPDLSCs as UECM enhances their biological functions.

LncRNA TUG1 mediates lipopolysaccharide-induced proliferative inhibition and apoptosis of human periodontal ligament cells by sponging miR-132

Emerging evidence shows that the long noncoding RNA taurine-upregulated gene 1 (TUG1) plays pivotal roles in regulating biological properties and functions of parenchyma cells in various types of disease processes. However, the mechanism underlying the effects of TUG1 on cell proliferation and apoptosis of human periodontal ligament cells (PDLCs) in periodontitis is undefined. In this study, we explored the functions of TUG1 and its underlying mechanisms in the inflammatory process induced by Porphyromonas gingivalis-derived lipopolysaccharide (LPS) in PDLCs. Our results showed that TUG1 had a decreased expression in both periodontal ligament (PDL) tissues with periodontitis and PDLCs under a LPS-induced inflammatory condition, and TUG1 expression was negatively correlated with miR-132 expression in periodontitis-affected PDL tissues. Furthermore, we found that TUG1 overexpression in PDLCs alleviated LPS-induced proliferative inhibition and apoptosis promotion, while TUG1 knockdown had the opposite effect. In addition, miR-132 inhibitor alleviated TUG1 knockdown-induced inhibition of proliferation and increase of apoptosis in PDLCs under inflammatory conditions induced by LPS. These findings indicated that TUG1 has an enormous potential in regulating cell proliferation and apoptosis of PDLCs during periodontitis and may provide an effective therapeutic target for periodontitis to reduce the damage caused by inflammatory reactions.

Characteristic differences of cell sheets composed of mesenchymal stem cells with different tissue origins

INTRODUCTION

Stem cell therapy with mesenchymal stem cells (MSCs) has been widely used in many clinical trials, and therapy with MSC sheets shows promise for patients. However, there are few reports characterizing MSC sheets. In the present study, the properties of MSC sheets derived from bone marrow, adipose tissue, and umbilical cord were evaluated.

METHODS

Cell sheets were fabricated with MSCs from different tissue origins in temperature-responsive cell culture dishes with and without pre-coating of fetal bovine serum (FBS). MSC adhesion behavior in the culture dish was observed. Secretion of cytokines related to cell proliferation and immune regulation from MSC sheets was investigated by ELISA. The adhesion properties of the MSC sheets were investigated by time-lapse microscopy.

RESULTS

Different cell adhesion and proliferation rates in temperature-responsive cell culture dishes were observed among the three types of MSCs. FBS pre-coating of the dishes enhanced cell attachment and proliferation in all cell types. Harvested cell sheets showed high attachment capacity to tissue culture polystyrene dish surfaces.

CONCLUSIONS

MSC sheets can be fabricated from MSCs from different tissue origins using temperature-responsive cell culture dishes. The fabricated MSC sheets could be useful in cell transplantation therapies by choosing appropriate types of MSCs that secrete therapeutic cytokines for the targeted diseases.

Human mesenchymal stem cell sheets in xeno-free media for possible allogenic applications

Cell-based therapies are increasingly focused on allogeneic stem cell sources because of several advantages in eliminating donor variability (e.g., aging and disease pathophysiology) affecting stem cell quality and in cell-banked sourcing of healthy donors to enable “off-the-shelf” products. However, allogeneic cell therapy is limited by host patient immunologic competence and inconsistent performance due to cell delivery methods. To address allogeneic cell therapy limitations, this study developed a new allogeneic stem cell sheet using human umbilical cord mesenchymal stem cells (hUC-MSC) that present low antigenicity (i.e., major histocompatibility complex, MHC). Optimal conditions including cell density, passage number, and culture time were examined to fabricate reliable hUC-MSC sheets. MHC II antigens correlated to alloimmune rejection were barely expressed in hUC-MSC sheets compared to other comparator MSC sheets (hBMSC and hADSC). hUC-MSC sheets easily graft spontaneously onto subcutaneous tissue in immune-deficient mice within 10 minutes of placement. No sutures are required to secure sheets to tissue because sheet extracellular matrix (ECM) actively facilitates cell-target tissue adhesion. At 10 days post-transplantation, hUC-MSC sheets remain on ectopic target tissue sites and exhibit new blood vessel formation. Furthermore, implanted hUC-MSC sheets secrete human HGF continuously to the murine target tissue. hUC-MSC sheets described here should provide new insights for improving allogenic cell-based therapies.

Pulsatile tubular cardiac tissues fabricated by wrapping human iPS cells-derived cardiomyocyte sheets

The purpose of this study was to fabricate pulsatile tubular cardiac tissue using cell sheet based-tissue engineering. First, we fabricated human induced pluripotent stem cell (hiPSc)-derived cardiomyocyte sheets and normal human dermal fibroblast (NHDF) sheets which are harvested from temperature responsive culture dishes only by lowering the temperature. Then tubular cardiac tissues are formed by wrapping one hiPSc-derived cardiomyocyte sheet and three NHDF sheets around an octagonal column, and both ends of the tubular tissue were covered with fibrin and collagen gel. The octagonal column with the tubular tissue was connected to an in vitro circulation system in a culture box. After four-day culture, the cardiac tissue survived and pulsated spontaneously in the circulation system. Furthermore, the analysis with a Millar catheter inserted into the cardiac tubes revealed significant inner pressure changes generated by their beating. In addition, the tubular cardiac tissue pulsated in response to the electrical stimulation. Although histological analyses demonstrated that cardiac troponin T-positive cells stratified the inner surface of the tubular tissues, gene expression analyses showed an immature state of these cardiomyocytes. Thus, cell sheet-based tissue engineering realized human pulsatile tubular cardiac tissue fabrication and we believe that these tubular cardiac tissues should contribute to future drug screening and regenerative therapy for heart diseases.

A systematic sequencing-based approach for microbial contaminant detection and functional inference

Background

Microbial contamination poses a major difficulty for successful data analysis in biological and biomedical research. Computational approaches utilizing next-generation sequencing (NGS) data offer promising diagnostics to assess the presence of contaminants. However, as host cells are often contaminated by multiple microorganisms, these approaches require careful attention to intra- and interspecies sequence similarities, which have not yet been fully addressed.

Results

We present a computational approach that rigorously investigates the genomic origins of sequenced reads, including those mapped to multiple species that have been discarded in previous studies. Through the analysis of large-scale synthetic and public NGS samples, we estimate that 1000–100,000 contaminating microbial reads are detected per million host reads sequenced by RNA-seq. The microbe catalog we established included Cutibacterium as a prevalent contaminant, suggesting that contamination mostly originates from the laboratory environment. Importantly, by applying a systematic method to infer the functional impact of contamination, we revealed that host-contaminant interactions cause profound changes in the host molecular landscapes, as exemplified by changes in inflammatory and apoptotic pathways during Mycoplasma infection of lymphoma cells.

Conclusions

We provide a computational method for profiling microbial contamination on NGS data and suggest that sources of contamination in laboratory reagents and the experimental environment alter the molecular landscape of host cells leading to phenotypic changes. These findings reinforce the concept that precise determination of the origins and functional impacts of contamination is imperative for quality research and illustrate the usefulness of the proposed approach to comprehensively characterize contamination landscapes.

Electronic supplementary material

The online version of this article (10.1186/s12915-019-0690-0) contains supplementary material, which is available to authorized users.

Stem cell-based bone and dental regeneration: a view of microenvironmental modulation

In modern medicine, bone and dental loss and defects are common and widespread morbidities, for which regenerative therapy has shown great promise. Mesenchymal stem cells, obtained from various sources and playing an essential role in organ development and postnatal repair, have exhibited enormous potential for regenerating bone and dental tissue. Currently, mesenchymal stem cells (MSCs)-based bone and dental regeneration mainly includes two strategies: the rescue or mobilization of endogenous MSCs and the application of exogenous MSCs in cytotherapy or tissue engineering. Nevertheless, the efficacy of MSC-based regeneration is not always fulfilled, especially in diseased microenvironments. Specifically, the diseased microenvironment not only impairs the regenerative potential of resident MSCs but also controls the therapeutic efficacy of exogenous MSCs, both as donors and recipients. Accordingly, approaches targeting a diseased microenvironment have been established, including improving the diseased niche to restore endogenous MSCs, enhancing MSC resistance to a diseased microenvironment and renormalizing the microenvironment to guarantee MSC-mediated therapies. Moreover, the application of extracellular vesicles (EVs) as cell-free therapy has emerged as a promising therapeutic strategy. In this review, we summarize current knowledge regarding the tactics of MSC-based bone and dental regeneration and the decisive role of the microenvironment, emphasizing the therapeutic potential of microenvironment-targeting strategies in bone and dental regenerative medicine.

Keratinocyte sheets prepared with temperature-responsive dishes show enhanced survival after in vivo grafting on acellular dermal matrices in a rat model of staged bi-layered skin reconstruction

Introduction

Bi-layered skin reconstruction can be achieved by staged grafting of acellular dermal matrices (ADMs) and cultured epithelial keratinocyte sheets (KSs). Both KSs and ADMs have been used for long; yet, their combined use has shown poor effectiveness. This outcome has been related to the enzymatic treatment used in the preparation of KSs, which impairs their adhesion potential to ADMs and the formation of a basement membrane (BM). Temperature-responsive (TR) culture dishes allow for enzyme-free preparation of KSs with preservation of BMs and intercellular adhesion proteins; yet, their use has not been previously applied to staged bi-layered skin reconstruction. Using an in vivo rat model, we tested the hypothesis that TR cultures enhance KSs survival and BM preservation after sequential grafting on ADMs.

Methods

In nude rats (n = 9/group), a 9-cm [2] full-thickness dorsal skin defect was repaired with a commercial ADM. At 2 weeks after surgery, we grafted the ADM with KSs (circular, 25 mm diameter), prepared from human cells either by enzymatic Dispase treatment (DT control group) or a TR culture dish (TR experimental group). KSs survival and BMs preservation was assessed one week later by digital imaging, histology (hematoxylin & eosin), immunohistochemistry (collagen IV, pancytokeratins) and immunofluorescence (cytokeratin 1-5-6, laminin).

Results

The TR group showed a significantly higher KSs survival (120 ± 49 vs. 63 ± 42 mm²; p < 0.05) and epidermal thickness (165 ± 79 vs. 65 ± 54 μm; p < 0.01) compared with the control DT group, as well as higher epidermal maturation (cytokeratin) and a denser laminin and Collagen IV expression in the BMs in vitro and in vivo.

Conclusion

These findings suggest that KSs prepared with TR culture dishes have significantly enhanced survival when grafted on ADMs; these outcomes could help improve current clinical strategies in wound care by skin reconstruction.

Using cell sheets to regenerate mouse submandibular glands

Temperature-responsive polymer grafted tissue culture dishes release cells as confluent living sheets in response to small changes in temperature, with recovered cell sheets retaining cell-cell communications, functional extracellular matrices and tissue-like behaviors. These features promote tissue regeneration and improve transplantation efficacy in various tissues including cartilage, heart, kidney, liver, endometrium, cornea, middle ear, periodontium, and esophageal living sheet transplants. However, the functional effects of cell sheets for salivary gland regeneration to treat hyposalivation have not yet been studied. Thus, the present study aims to both establish the viability of thermoresponsive cell sheets for use in salivary glands and then explore the delivery option (i.e., single vs. multiple layers) that would result in the most complete tissue growth in terms of cell differentiation and recovered tissue integrity. Results indicate that single cell sheets form polarized structures that maintain cell-cell junctions and secretory granules in vitro while layering of two-single cell sheets forms a glandular-like pattern in vitro. Moreover, double layer cell sheets enhance tissue formation, cell differentiation and saliva secretion in vivo. In contrast, single cell sheets demonstrated only modest gains relative to the robust growth seen with the double layer variety. Together, these data verify the utility of thermoresponsive cell sheets for use in salivary glands and indicates the double layer form to provide the best option in terms of cell differentiation and recovered tissue integrity, thereby offering a potential new therapeutic strategy for treating hyposalivation.

Extracellular Matrix Induces Periodontal Ligament Reconstruction In Vivo

One of the problems in dental implant treatment is the lack of periodontal ligament (PDL), which supports teeth, prevents infection, and transduces sensations such as chewiness. The objective of the present study was to develop a decellularized PDL for supporting an artificial tooth. To this end, we prepared mouse decellularized mandible bone with a PDL matrix by high hydrostatic pressure and DNase and detergent treatments and evaluated its reconstruction in vivo. After tooth extraction, the decellularized mandible bone with PDL matrix was implanted under the subrenal capsule in rat and observed that host cells migrated into the matrix and oriented along the PDL collagen fibers. The extracted decellularized tooth and de- and re-calcified teeth, which was used as an artificial tooth model, were re-inserted into the decellularized mandible bone and implanted under the subrenal capsule in rat. The reconstructed PDL matrix for the extracted decellularized tooth resembled the decellularized mandible bone without tooth extraction. This demonstrates that decellularized PDL matrix can reconstruct PDL tissue by controlling host cell migration, which could serve as a novel periodontal treatment approach.

Application of cell-sheet engineering for new formation of cementum around dental implants

Periodontal disease involves the chronic inflammation of tooth supporting periodontal tissues. As the disease progresses, it manifests destruction of periodontal tissues and eventual tooth loss. The regeneration of lost periodontal tissue has been one of the most important subjects in periodontal research. Since their discovery, periodontal ligament stem cells (PDLSCs), have been transplanted into periodontal bony defects to examine their regenerative potential. Periodontal defects were successfully regenerated using PDLSC sheets, which were fabricated by cell sheet engineering in animal models, and for which clinical human trials are underway. To expand the utility of PDLSC sheet, we attempted to construct periodontal tissues around titanium implants with the goal of facilitating the prevention of peri-implantitis. In so doing, we found newly formed cementum-periodontal ligament (PDL) structures on the implant surface. In this mini review, we summarize the literature regarding cell-based periodontal regeneration using PDLSCs, as well as previous trials aimed at forming periodontal tissues around dental implants. Moreover, the recent findings in cementogenesis are reviewed from the perspective of the formation of further stable periodontal attachment structure on dental implant. This mini review aims to summarize the current status of the creation of novel periodontal tissue-bearing dental implants, and to consider its future direction.

Analysis of human nasal mucosal cell sheets fabricated using transported tissue and blood specimens

Previously, we succeeded in transplanting autologous nasal mucosal cell sheets in the middle ears of 5 patients, who underwent cholesteatoma resection, which prevents recurrence of cholesteatoma in clinical settings. Current good manufacturing practice (GMP) standards for human cell cultivation requires the establishment of cell processing centers (CPC) which act as germ-free facilities. However, due to practical difficulties involved in establishing and maintaining such facilities at each individual hospital, a functional transport system is felt to be needed for the continuation of effective regenerative therapy. In the current study, nasal mucosal tissue and autologous blood obtained from 3 human volunteers were transported for over 3 h. Disinfected nasal tissues were cultured using keratinocyte culture medium, which included autologous serum prepared from blood. After 24 d, cultured nasal mucosal cells were transported for over 3 h and subsequently assessed for cell number, viability and purity. Moreover, CK4, CK8, and CK18 were analyzed the suitability of these nasal mucosal cell sheets for middle ear regenerative therapy.

Overall, we confirmed that nasal mucosal cell sheets can be fabricated using transported nasal mucosal tissue and blood. This study would be contribute to establish a new regenerative therapy for clinical application, accompanied with transportation between companies and hospitals.

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Transportation of nasal mucosal tissue and blood.

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Characterizing of nasal mucosal cell sheet by immunohistology.

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Transportation of nasal mucosal cell sheet as pre-clinical study.

Amnion-derived cells as a reliable resource for next-generation regenerative medicine

The placenta is composed of the amnion, chorionic plate, villous and smooth chorion, decidua basalis, and umbilical cord. The amnion is a readily obtainable source of a large number of cells and cell types, including epithelium, mesenchyme, and endothelium, and is thus an allogeneic resource for regenerative medicine. Endothelial cells are obtained from large arteries and veins in the amniotic membrane as well as the umbilical cord. The amnion-derived cells exhibit transdifferentiation capabilities, including chondrogenesis and cardiomyogenesis, by introduction of transcription factors, in addition to their original and potential phenotypes. The amnion is also a source for production of induced pluripotent stem cells (AM-iPSCs). The AM-iPSCs exhibit stable phenotypes, such as multipotency and immortality, and a unique gene expression pattern. Through the use of amnion-derived cells, as well as other placenta-derived cells, preclinical proof of concept has been achieved in a mouse model of muscular dystrophy.

Application of Periodontal Ligament-Derived Multipotent Mesenchymal Stromal Cell Sheets for Periodontal Regeneration

Periodontitis is a chronic inflammatory disorder that causes destruction of the periodontal attachment apparatus including alveolar bone, the periodontal ligament, and cementum. Dental implants have been routinely installed after extraction of periodontitis-affected teeth; however, recent studies have indicated that many dental implants are affected by peri-implantitis, which progresses rapidly because of the failure of the immune system. Therefore, there is a renewed focus on periodontal regeneration aroundnatural teeth. To regenerate periodontal tissue, many researchers and clinicians have attempted to perform periodontal regenerative therapy using materials such as bioresorbable scaffolds, growth factors, and cells. The concept of guided tissue regeneration, by which endogenous periodontal ligament- and alveolar bone-derived cells are preferentially proliferated by barrier membranes, has proved effective, and various kinds of membranes are now commercially available. Clinical studies have shown the significance of barrier membranes for periodontal regeneration; however, the technique is indicated only for relatively small infrabony defects. Cytokine therapies have also been introduced to promote periodontal regeneration, but the indications are also for small size defects. To overcome this limitation, ex vivo expanded multipotent mesenchymal stromal cells (MSCs) have been studied. In particular, periodontal ligament-derived multipotent mesenchymal stromal cells are thought to be a responsible cell source, based on both translational and clinical studies. In this review, responsible cell sources for periodontal regeneration and their clinical applications are summarized. In addition, recent transplantation strategies and perspectives about the cytotherapeutic use of stem cells for periodontal regeneration are discussed.

Recent Advances in Engineered Stem Cell-Derived Cell Sheets for Tissue Regeneration

The substantial progress made in the field of stem cell-based therapy has shown its significant potential applications for the regeneration of defective tissues and organs. Although previous studies have yielded promising results, several limitations remain and should be overcome for translating stem cell-based therapies to clinics. As a possible solution to current bottlenecks, cell sheet engineering (CSE) is an efficient scaffold-free method for harvesting intact cell sheets without the use of proteolytic enzymes, and may be able to accelerate the adoption of stem cell-based treatments for damaged tissues and organs regeneration. CSE uses a temperature-responsive polymer-immobilized surface to form unique, scaffold-free cell sheets composed of one or more cell layers maintained with important intercellular junctions, cell-secreted extracellular matrices, and other important cell surface proteins, which can be achieved by changing the surrounding temperature. These three-dimensional cell sheet-based tissues can be designed for use in clinical applications to target-specific tissue regeneration. This review will highlight the principles, progress, and clinical relevance of current approaches in the cell sheet-based technology, focusing on stem cell-based therapies for bone, periodontal, skin, and vascularized muscles.

Exosomes derived from clinical-grade oral mucosal epithelial cell sheets promote wound healing

The oral mucosa exhibits unique regenerative properties, sometimes referred to as foetal-like wound healing. Researchers from our institute have used sheets of oral mucosa epithelial cells (OMECs) for regenerative medicine applications including cornea replacement and oesophageal epithelial regeneration for stricture prevention. Here, we have isolated exosomes from clinical-grade production of OMEC sheets from healthy human donors (n = 8), aiming to evaluate the clinical potential of the exosomes to stimulate epithelial regeneration and to improve understanding of the mode-of-action of the cells. Exosomes were isolated from conditioned (cExo) and non-conditioned (ncExo) media. Characterization was performed using Western blot for common exosomal-markers: CD9 and flotillin were positive while annexin V, EpCam and contaminating marker GRP94 were negative. Nanoparticle tracking analysis revealed a diameter of ~120 nm and transmission electron microscopy showed a corresponding size and spherical appearance. Human skin fibroblasts exposed to exosomes showed dose-dependent reduction of proliferation and a considerable increase of growth factor gene expression (HGF, VEGFA, FGF2 and CTGF). The results were similar for both groups, but with a trend towards a larger effect from cExo. To study adhesion, fluorescently labelled exosomes were topically applied to pig oesophageal wound-beds ex vivo and subsequently washed. Positive signal could be detected after as little as 1 min of adhesion, but increased adhesion time produced a stronger signal. Next, labelled exosomes were added to full-thickness skin wounds in rats and signal was detected up to 5 days after application. cExo significantly reduced the wound size at days 6 and 17. In conclusion, exosomes from OMEC sheets showed pro-regenerative effects on skin wound healing. This is the first time that the healing capacity of the oral mucosa is studied from an exosome perspective. These findings might lead to a combinational therapy of cell sheets and exosomes for future patients with early oesophageal cancer.