Potential of induced pluripotent stem cells for the regeneration of the tracheal wall

Transplantation of a 3D-printed tracheal graft combined with iPS cell-derived MSCs and chondrocytes

For successful tracheal reconstruction, tissue-engineered artificial trachea should meet several requirements, such as biocompatible constructs comparable to natural trachea, coverage with ciliated respiratory mucosa, and adequate cartilage remodeling to support a cylindrical structure. Here, we designed an artificial trachea with mechanical properties similar to the native trachea that can enhance the regeneration of tracheal mucosa and cartilage through the optimal combination of a two-layered tubular scaffold and human induced pluripotent stem cell (iPSC)-derived cells. The framework of the artificial trachea was fabricated with electrospun polycaprolactone (PCL) nanofibers (inner) and 3D-printed PCL microfibers (outer). Also, human bronchial epithelial cells (hBECs), iPSC-derived mesenchymal stem cells (iPSC-MSCs), and iPSC-derived chondrocytes (iPSC-Chds) were used to maximize the regeneration of tracheal mucosa and cartilage in vivo. After 2 days of cultivation using a bioreactor system, tissue-engineered artificial tracheas were transplanted into a segmental trachea defect (1.5-cm length) rabbit model. Endoscopy did not reveal granulation ingrowth into tracheal lumen. Alcian blue staining clearly showed the formation of ciliated columnar epithelium in iPSC-MSC groups. In addition, micro-CT analysis showed that iPSC-Chd groups were effective in forming neocartilage at defect sites. Therefore, this study describes a promising approach for long-term functional reconstruction of a segmental tracheal defect.

Retention of Human-Induced Pluripotent Stem Cells (hiPS) With Injectable HA Hydrogels for Vocal Fold Engineering

Objective:

One prospective treatment option for vocal fold scarring is regeneration with an engineered scaffold containing induced pluripotent stem cells (iPS). In the present study, we investigated the feasibility of utilizing an injectable hyaluronic acid (HA) scaffold encapsulated with human-iPS cell (hiPS) for regeneration of vocal folds.

Methods:

Thirty athymic nude rats underwent unilateral vocal fold injury. Contralateral vocal folds served as uninjured controls. Hyaluronic acid hydrogel scaffold, HA hydrogel scaffold containing hiPS, and HA hydrogel scaffold containing hiPS with epidermal growth factor (EGF) were injected in both vocal folds immediately after surgery. One and 2 weeks after injection, larynges were excised for histology, immunohistochemistry, and fluorescence in situ hybridization (FISH).

Results:

Presence of HA hydrogel was confirmed in vocal folds 1 and 2 weeks post injection. The FISH analysis confirmed the presence and viability of hiPS in the injected vocal folds. Histological results demonstrated that vocal folds injected with HA hydrogel scaffold containing EGF demonstrated less fibrosis than those with HA hydrogel only.

Conclusions:

Human-iPS survived in injured rat vocal folds. The HA hydrogel with hiPS and EGF ameliorated the fibrotic response. Additional work is necessary to optimize hiPS differentiation and further confirm the safety of hiPS for clinical applications.

Regeneration of tracheal epithelium using mouse induced pluripotent stem cells

Conclusion The findings demonstrated the potential use of induced pluripotent stem cells for regeneration of tracheal epithelium. Objective Autologous tissue implantation techniques using skin or cartilage are often applied in cases of tracheal defects with laryngeal inflammatory lesions and malignant tumor invasion. However, these techniques are invasive with an unstable clinical outcome. The purpose of this study was to investigate regeneration in a tracheal defect site of nude rats after implantation of ciliated epithelium that was differentiated from induced pluripotent stem cells. Method Embryoid bodies were formed from mouse induced pluripotent stem cells. They were cultured with growth factors for 5 days, and then cultured at the air-liquid interface. The degree of differentiation achieved prior to implantation was determined by histological findings and the results of real-time polymerase chain reaction. Embryoid bodies including ciliated epithelium were embedded into collagen gel that served as an artificial scaffold, and then implanted into nude rats, creating an 'air-liquid interface model'. Histological evaluation was performed 7 days after implantation. Results The ciliated epithelial structure survived on the lumen side of regenerated tissue. It was demonstrated histologically that the structure was composed of ciliated epithelial cells.

In vitro epithelial differentiation of human induced pluripotent stem cells for vocal fold tissue engineering

OBJECTIVES

We determined the feasibility and optimization of differentiating human induced pluripotent stem cells (hiPS) into nonkeratinized stratified squamous epithelial cells for vocal fold engineering.

METHODS

hiPS were cultured and assessed for differentiation in 3 conditions: a 3-dimensional (3D) hyaluronic acid (HA) hydrogel scaffold, a 3D HA hydrogel scaffold with epidermal growth factor (EGF), and a 3D HA hydrogel scaffold cocultured with human vocal fold fibroblasts (hVFF). After 1, 2, and 4 weeks of cultivation, hiPS were selected for histology, immunohistochemistry, and/or transcript expression analysis.

RESULTS

At 4 weeks, hiPS cultivated with hVFF or with EGF had significantly decreased levels of Oct 3/4, indicating loss of pluripotency. Immunofluorescence revealed the presence of pancytokeratin and of cytokeratin (CK) 13 and 14 epithelial-associated proteins at 4 weeks after cultivation in hiPS EGF and hiPS hVFF cultures. The transcript expression level of CK14 was significantly increased for hiPS hVFF cultures only and was measured concomitantly with cell morphology that was clearly cohesive and displayed a degree of nuclear polarity suggestive of epithelial differentiation.

CONCLUSIONS

We found that hiPS cultivated in 3D HA hydrogel with hVFF demonstrated the most robust conversion evidence to date of epithelial differentiation. Further work is necessary to focus on amplification of these progenitors for application in vocal fold regenerative biology.

Effective embryoid body formation from induced pluripotent stem cells for regeneration of respiratory epithelium

OBJECTIVES/HYPOTHESIS

We have previously demonstrated the potential use of induced pluripotent stem (iPS) cells for regeneration of respiratory epithelium by culturing embryoid bodies (EBs). The aim of the present study was to determine the most effective conditions for EB formation from iPS cells for regeneration of respiratory epithelium.

STUDY DESIGN

Experimental study.

METHODS

iPS cells cultured on a gelatin-coated dish were seeded on low-attachment plates for generating EBs. Under several conditions including the air-liquid interface (ALI) method, with varying cell numbers and suspension times, EBs were transferred to a gelatin-coated dish supplemented with growth factors. The shape, size, aggregation, and adhesion of EBs for iPS cell differentiation were evaluated, and the cultured tissue was histologically examined.

RESULTS

EBs appropriate for differentiation were observed using 1,000 cells after 5 days of suspension culture. Respiratory epithelium-like tissue was histologically observed. The ciliary epithelium was confirmed immunohistologically.

CONCLUSIONS

Based on the varying suspension times and cell numbers with the ALI method, this study presented effective conditions for EB formation from iPS cells for regeneration of respiratory epithelium.

Cell sources for trachea tissue engineering: past, present and future

Trachea tissue engineering has been one of the most promising approaches to providing a potential clinical application for the treatment of long-segment tracheal stenosis. The sources of the cells are particularly important as the primary factor for tissue engineering. The use of appropriate cells seeded onto scaffolds holds huge promise as a means of engineering the trachea. Furthermore, appropriate cells would accelerate the regeneration of the tissue even without scaffolds. Besides autologous mature cells, various stem cells, including bone marrow-derived mesenchymal stem cells, adipose tissue-derived stem cells, umbilical cord blood-derived mesenchymal stem cells, amniotic fluid stem cells, embryonic stem cells and induced pluripotent stem cells, have received extensive attention in the field of trachea tissue engineering. Therefore, this article reviews the progress on different cell sources for engineering tracheal cartilage and epithelium, which can lead to a better selection and strategy for engineering the trachea.

Novel additive manufactured scaffolds for tissue engineered trachea research

CONCLUSIONS

This study demonstrates proof of concept for controlled manufacturing methods that utilize novel tailored biopolymers (3D photocuring technology) or conventional bioresorbable polymers (fused deposition modeling, FDM) for macroscopic and microscopic geometry control. The manufactured scaffolds could be suitable for tissue engineering research.

OBJECTIVES

To design novel trachea scaffold prototypes for tissue engineering purposes, and to fabricate them by additive manufacturing.

METHODS

A commercial 3D model and CT scans of a middle-aged man were obtained for geometrical observations and measurements of human trachea. Model trachea scaffolds with variable wall thickness, interconnected pores, and various degrees of porosity were designed. Photocurable polycaprolactone (PCL) polymer was used with 3D photocuring technology. Thermoplastic polylactide (PLA) and PCL were used with FDM. Cell cultivations were performed for biocompatibility studies.

RESULTS

Scaffolds of various sizes and porosities were successfully produced. Both thermoplastic PLA and PCL and photocurable PCL could be used effectively with additive manufacturing technologies to print high-quality tubular porous biodegradable structures. Optical microscopic and SEM images showed the viability of cells. The cells were growing in multiple layers, and biocompatibility of the structures was shown.

Implantation site-dependent differences for tracheal regeneration with induced pluripotent stem cells (iPS cells)

CONCLUSION

The histological findings and quantitative measurements demonstrated that there were differences in teratoma formation according to the site of implantation. Elucidating the mechanisms of the teratoma formation caused by the site of implantation moves the field another step closer to clinical use of induced pluripotent stem (iPS) cells for tracheal regeneration.

OBJECTIVES

Our previous study demonstrated the potential for iPS cells to be used as a new cell source for tracheal regeneration. However, teratoma formation remains a major problem. Implantation site-dependent differences in teratoma formation have been reported. In this study, the teratoma-forming propensity after implantation into tracheal defects and abdominal subcutaneous tissue was examined histologically and quantitatively.

METHODS

Mouse iPS cells were cultured in artificial material under various conditions. After cultivation in vitro, artificial materials with cultured iPS cells were then implanted into cervical tissue around tracheal defects and into abdominal subcutaneous tissue in nude rats. Teratoma formation was evaluated histologically and quantitatively with measurement of maximum diameter (MD).

RESULTS

Teratoma was observed in 10 of 11 rats with cervical tissue around tracheal defects and in 3 of 11 rats with abdominal subcutaneous tissue implants. The average MD was 5.36 mm in the trachea and 0.97 mm in the abdomen.

Systematic Review of Induced Pluripotent Stem Cell Technology as a Potential Clinical Therapy for Spinal Cord Injury

Transplantation therapies aimed at repairing neurodegenerative and neuropathological conditions of the central nervous system (CNS) have utilized and tested a variety of cell candidates, each with its own unique set of advantages and disadvantages. The use and popularity of each cell type is guided by a number of factors including the nature of the experimental model, neuroprotection capacity, the ability to promote plasticity and guided axonal growth, and the cells' myelination capability. The promise of stem cells, with their reported ability to give rise to neuronal lineages to replace lost endogenous cells and myelin, integrate into host tissue, restore functional connectivity, and provide trophic support to enhance and direct intrinsic regenerative ability, has been seen as a most encouraging step forward. The advent of the induced pluripotent stem cell (iPSC), which represents the ability to “reprogram” somatic cells into a pluripotent state, hails the arrival of a new cell transplantation candidate for potential clinical application in therapies designed to promote repair and/or regeneration of the CNS. Since the initial development of iPSC technology, these cells have been extensively characterized in vitro and in a number of pathological conditions and were originally reported to be equivalent to embryonic stem cells (ESCs). This review highlights emerging evidence that suggests iPSCs are not necessarily indistinguishable from ESCs and may occupy a different “state” of pluripotency with differences in gene expression, methylation patterns, and genomic aberrations, which may reflect incomplete reprogramming and may therefore impact on the regenerative potential of these donor cells in therapies. It also highlights the limitations of current technologies used to generate these cells. Moreover, we provide a systematic review of the state of play with regard to the use of iPSCs in the treatment of neurodegenerative and neuropathological conditions. The importance of balancing the promise of this transplantation candidate in the light of these emerging properties is crucial as the potential application in the clinical setting approaches. The first of three sections in this review discusses (A) the pathophysiology of spinal cord injury (SCI) and how stem cell therapies can positively alter the pathology in experimental SCI. Part B summarizes (i) the available technologies to deliver transgenes to generate iPSCs and (ii) recent data comparing iPSCs to ESCs in terms of characteristics and molecular composition. Lastly, in (C) we evaluate iPSC-based therapies as a candidate to treat SCI on the basis of their neurite induction capability compared to embryonic stem cells and provide a summary of available in vivo data of iPSCs used in SCI and other disease models.

Potential for Respiratory Epithelium Regeneration from Induced Pluripotent Stem Cells

Objectives:

In cases of laryngeal inflammatory lesions and tracheal invasion of a malignant tumor, autologous tissue implantation techniques using skin or cartilage are often applied. However, these techniques are both invasive and unstable. The purpose of this study was to evaluate the potential use of induced pluripotent stem (iPS) cells in the regeneration of respiratory epithelium.

Methods:

We seeded iPS cells on low-attachment plates in serum-free media to generate embryoid bodies (EBs). After a 3-day culture, the EBs were transferred to a gelatin-coated dish supplemented with activin A alone or with basic fibroblast growth factor (induction groups). As a control, EBs were cultured without these growth factors (control group). Cultured tissues from all groups were histologically examined for 2 weeks.

Results:

In the induction groups, the presence of respiratory epithelium-like tissue was observed with hematoxylin and eosin staining after 14 days of culture.

Conclusions:

This study demonstrated the potential use of iPS cells in regeneration of the respiratory epithelium.

Evaluation of the use of induced pluripotent stem cells (iPSCs) for the regeneration of tracheal cartilage

The treatment of laryngotracheal stenosis remains a challenge as treatment often requires multistaged procedures, and successful decannulation sometimes fails after a series of operations. Induced pluripotent stem cells (iPSCs) were generated in 2006. These cells are capable of unlimited symmetrical self-renewal, thus providing an unlimited cell source for tissue-engineering applications. We have previously reported tracheal wall regeneration using a three-dimensional (3D) scaffold containing iPSCs. However, the efficiency of differentiation into cartilage was low. In addition, it could not be proven that the cartilage tissues were in fact derived from the implanted iPSCs. The purpose of this study was to evaluate and improve the use of iPSCs for the regeneration of tracheal cartilage. iPSCs were cultured in vitro in a 3D scaffold in chondrocyte differentiation medium. After cultivation, differentiation into chondrocytes was examined. The ratio of undifferentiated cells was analyzed by flow cytometry. The 3D scaffolds were implanted into tracheal defects, as an injury site, in 24 nude rats. Differentiation into chondrocytes in vitro was confirmed histologically, phenotypically, and genetically. Flow cytometric analysis demonstrated that the population of undifferentiated cells was decreased. Cartilage tissue was observed in the regenerated tracheal wall in 6 of 11 rats implanted with induced iPSCs, but in none of 13 rats implanted with the control and noninduced iPSCs. The expression of cartilage-specific protein was also demonstrated in vivo in 3D scaffolds containing iPSCs. The presence of the GFP gene derived from iPSCs was confirmed in samples of cartilage tissue by the combination of laser microdissection (LMD) and polymerase chain reaction (PCR) techniques. Our study demonstrated that iPSCs have the potential to differentiate into chondrogenic cells in vitro. Cartilage tissue was regenerated in vivo. Our results suggest that iPSCs could be a new cell source for the regeneration of tracheal cartilage.

Collagen vitrigel scaffold for regenerative medicine of the trachea: experimental study and quantitative evaluation

CONCLUSION

Our technique for tracheal regeneration using a collagen vitrigel scaffold affords a feasible approach for accelerating epithelial regeneration on the intraluminal surface of the host tracheal defect.

OBJECTIVES

The purpose of the study was to quantitatively evaluate the effectiveness of a collagen vitrigel scaffold for the regeneration of the tracheal epithelium.

METHODS

The collagen vitrigel scaffold was developed by conjugating a collagen vitrigel membrane to a collagen sponge to promote both epithelial cell growth and mesenchymal cell infiltration. The collagen vitrigel scaffold was implanted into tracheal defects in rats as the vitrigel model, and a conventional collagen sponge was implanted as a control model. The structure of the regenerated tissue was observed and thickness of the epithelium was quantitatively evaluated by histological examination.

RESULTS

Histological findings showed the surface of the collagen vitrigel scaffold to be flat in comparison with that of the conventional collagen sponge. At 7, 14, and 28 days post-implantation, the average thickness of the regenerated epithelial layer in the vitrigel model group was greater than that in the control group.

Chondrogenesis and cartilage tissue engineering: the longer road to technology development

Joint injury and disease are painful and debilitating conditions affecting a substantial proportion of the population. The idea that damaged cartilage in articulating joints might be replaced seamlessly with tissue-engineered cartilage is of obvious commercial interest because the market for such treatments is large. Recently, a wealth of new information about the complex biology of chondrogenesis and cartilage has emerged from stem cell research, including increasing evidence of the role of physical stimuli in directing differentiation. The challenge for the next generation of tissue engineers is to identify the key elements in this new body of knowledge that can be applied to overcome current limitations affecting cartilage synthesis in vitro. Here we review the status of cartilage tissue engineering and examine the contribution of stem cell research to technology development for cartilage production.

Tracheobronchial bio-engineering: biotechnology fulfilling unmet medical needs

The development of substitutes for the human trachea or its bronchial tree represents a niche application in the rapidly advancing scientific field of Regenerative Medicine. Despite a comparatively small research foundation in the field of tracheo-bronchial bioengineering, four different approaches have already been translated into clinical settings and applied in patients. This can be attributed to the lack of established treatment options for a small group of patients with extensive major airway disease. In this review, the clinical background and tissue-specific basics of tracheo-bronchial bioengineering will be evaluated. Focusing on the clinical applications of bioengineered tracheal tissues, a "top-down" or "bedside-to-bench" analysis is performed in order to guide future basic and clinical research activities for airway bioengineering.