Seeding and Implantation of a Biosynthetic Tissue-engineered Tracheal Graft in a Mouse Model
Summary
Graft stenosis poses a critical obstacle in tissue engineered airway replacement. To investigate cellular mechanisms underlying stenosis, we utilize a murine model of tissue engineered tracheal replacement with seeded bone marrow mononuclear cells (BM-MNC). Here, we detail our protocol, including scaffold manufacturing, BM-MNC isolation, graft seeding, and implantation.
Abstract
Treatment options for congenital or secondary long segment tracheal defects have historically been limited due to an inability to replace functional tissue. Tissue engineering holds great promise as a potential solution with its ability to integrate cells and signaling molecules into a 3-dimensional scaffold. Recent work with tissue engineered tracheal grafts (TETGs) has seen some success but their translation has been limited by graft stenosis, graft collapse, and delayed epithelialization. In order to investigate the mechanisms driving these issues, we have developed a mouse model for tissue engineered tracheal graft implantation. TETGs were constructed using electrospun polymers polyethylene terephthalate (PET) and polyurethane (PU) in a mixture of PET and PU (20:80 percent weight). Scaffolds were then seeded using bone marrow mononuclear cells isolated from 6-8 week-old C57BL/6 mice by gradient centrifugation. Ten million cells per graft were seeded onto the lumen of the scaffold and allowed to incubate overnight before implantation between the third and seventh tracheal rings. These grafts were able to recapitulate the findings of stenosis and delayed epithelialization as demonstrated by histological analysis and lack of Keratin 5 and Keratin 14 basal epithelial cells on immunofluorescence. This model will serve as a tool for investigating cellular and molecular mechanisms involved in host remodeling.
Introduction
Long-segment tracheal defects can present as rare congenital conditions such as complete tracheal rings and tracheal agenesis, as well as trauma, malignancy, and infection. When exceeding 6 cm in adults or 30% of the tracheal length in children, these defects cannot be treated by surgical reconstruction. Attempts to replace the airway with autologous tissue, cadaveric transplants, and artificial constructs have been plagued by chronic infection, granulation, mechanical failure, and stenosis.
Tissue engineered tracheal grafts (TETGs) can potentially address these problems while avoiding the need for life-long immunosuppression. In the last decade, TETGs have been tested in animal models and utilized clinically in rare instances of compassionate use1,2,3. In both clinical and large animal studies, post-operative recovery from tissue engineered airway replacement required numerous interventions to combat stenosis (defined as >50% luminal narrowing) and maintain airway patency. Additional TETG work has sought to reduce this stenosis through evaluating the role of cell seeding choice, vascularization and scaffold design. Cell seeding choices and scaffold design aimed at restoring native trachea structure/function have mainly been focused on respiratory epithelial cells and chondrocytes seeded on various resorbable, non-resorbable and decellularized scaffolds. As vascularization likely plays an major role in the development of stenosis, other groups have focused on optimizing in vitro or heterotopic models to expedite revascularization or neoangiogenesis4. Nonetheless, achieving successful vascularization while also maintaining a mechanically competent and functional TETG remains a challenge. Despite recent advances, minimizing stenosis remains a critical obstacle to clinical translation.
To investigate this histopathological response to TETG implantation in vivo, we developed an ovine model of tissue engineered tracheal replacement. The graft was composed of a mixed polyethylene terephthalate (PET) and polyurethane (PU) electrospun scaffold seeded with bone marrow-derived mononuclear cells (BM-MNCs). In this small cohort, we demonstrated that seeded autologous BM-MNCs accelerated re-epithelialization and delayed stenosis5. Although seeding with autologous BM-MNCs improved survival, the cellular mechanism by which BM-MNCs modulate the formation of functional neotissue remains unclear.
Investigation on the cellular level required development of a murine model of tissue engineered tracheal replacement. Similar to the ovine study, we utilized a PET:PU electrospun scaffold seeded with BM-MNCs. Consistent with the ovine model, TETG stenosis developed over the course of the first two weeks following implantation1,2,3,5. This suggested that the murine model recapitulated the pathology observed previously, enabling us to further interrogate the cellular mechanisms underlying airway stenosis.
In this report, we detail our protocol for tissue engineered tracheal replacement in the mouse model including scaffold manufacturing, BM-MNC isolation, graft seeding, and implantation (Figure 1, Figure 2).
Protocol
Representative Results
Discussion
Development of a mouse model for tissue engineered tracheas is essential in understanding the factors that have limited clinical translation of the TETGs; namely graft collapse, stenosis and delayed epithelialization4. A few factors that contribute to these limitations include selection of graft material, the manufacturing process, scaffold design and cell seeding protocols. This model allows for faster evaluation of these factors in order to understand the cellular and molecular mechanisms affect…
Disclosures
The authors have nothing to disclose.
Acknowledgements
We would like to acknowledge Robert Strouse and the Research Information Solutions & Innovations division at Nationwide Children's Hospital for their support in graphic design. This work was supported by a grant from the NIH (NHLBI K08HL138460).
Materials
| 0.9% Sodium chloride injection | APP Pharmaceuticals | NDC 63323-186-10 | |
| 10cc serological pipet | Falcon | 357551 | |
| 18G 1.5in. Needle | BD | 305190 | |
| 1mL Syringe | BD | 309659 | |
| 24-well plate | Corning | 3526 | |
| 25cc serological pipet | Falcon | 356535 | |
| 25G 1in. Needle | BD | 305125 | |
| 50cc tube | BD | 352070 | |
| Alcohol prep pads | Fisher Healthcare | NDC 69250-661-02 | |
| Baytril (enrofloxacin) solution | Bayer Healthcare, LLC | NDC 0859-2267-01 | |
| Black polyamide monofilament suture, 9-0 | AROSurgical Instruments Corporation | T05A09N10-13 | |
| C57BL/6, female | Jackson laboratories | 664 | 6-8 weeks old |
| Citrate Buffer pH 6.0 20x concentrate | ThermoFisher | 5000 | |
| Colibri retractors | F.S.T | 17000-04 | |
| Cotton tipped applicators | Fisher scientific | 23-400-118 | |
| Cytokeratin 14 Monoclonal Antibody | ThermoFisher | MA5-11599 | |
| Dumont #5 Forceps | F.S.T | 11251-20 | |
| Dumont #5/45 forceps | F.S.T | 11251-35 | |
| Dumont #7 – Fine Forceps | F.S.T | 11274-20 | |
| F4/80 Rat anti-mouse antibody | Bio-Rad | MCA497R | |
| Ficoll | Sigma | 10831-100mL | |
| Fine scissors- Sharp-blunt | F.S.T | 14028-10 | |
| Fisherbrand Premium Cover Glasses | ThermoFisher | 12-548-5M | |
| Fluoroshield Mounting Media with DAPI | Abcam | ab104139 | |
| Goat-anti mouse IgG Secondary Antibody Alexa Fluor 594 | ThermoFisher | A-11001 | |
| Goat-anti Rabbit IgG Secondary Antibody Alexa Fluor 594 | ThermoFisher | A-11012 | |
| Goat-anti Rat IgG Secondary Antibody Alexa Fluor 647 | ThermoFisher | A-21247 | |
| Ibuprofen | Precision Dose, Inc | NDC 68094-494-59 | |
| Iodine prep pads | Professional disposables international, Inc. | NDC 10819-3883-1 | |
| Keratin 5 Polyclonal Antibody, Purified | BioLegend | 905501 | |
| Ketamine hydrochloride injection | Hospira Inc. | NDC 0409-2053 | |
| Micro-Adson forceps | F.S.T | 11018-12 | |
| Microscope | Leica | M80 | |
| Non-woven sponges | Covidien | 441401 | |
| Opthalmic ointment | Dechra Veterinary products | NDC 17033-211-38 | |
| PBS | Gibco | 10010-023 | |
| PET/PU (Polyethylene terephthalate & Polyurethane) scaffolds | Nanofiber solutions | Custom ordered | |
| Petri dish | BD | 353003 | |
| RPMI 1640 Medium | Gibco | 11875-093 | |
| TISH Needle Holder/Forceps | Micrins | MI1540 | |
| Trimmer | Wahl | 9854-500 | |
| Vannas-Tübingen Spring Scissors | F.S.T | 15008-08 | |
| Warm water recirculator | Gaymar | TP-700 | |
| Xylazine sterile solution | Akorn animal health | NDC 59399-110-20 |
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